D IG ITA L C O M PU T E R l - oot 04W iso OFFICE OF NAVAL RESEARCH • MATHEMATICAL SCIENCES DIVISION April 1953 Vol 5 No 2 TABLE OF CONTENTS 4 5 Naval Proving Ground Calculators Whirlwind 1 Computer Research Corporation Computers CADAC 10Z-A CRC 105 CRC 107 Moore School Automatic Computer MSAC Air Force Missile Test Center Computer FLAC 6 The SEAC I 2 3 7 8 9 10 I 12 13 14 15 The IAS Computer The SWAC The MONROBOT The Circle Computer The Jacobs Instrument Company Computers JAINCOMPS Consolidated Electronic Digital Computer Model 30-201 The ERA 1103 Computer The Rand Corporation Computer Aberdeen Proving Ground Computers DATA PROCESSING AND CONVERSION EOUIPMENT 1 Z 3 4 5 6 TELEDUCER SADIC Benson-Lehner Incremental Plotter Coleman Digitizer Ferro-Resonant Flip-Flop Logrinc Automatic Graph Followers LIST OF COMPUTING SERVICES COMPUTER AND NUMERICAL ANALYSIS COURSES I Massachusetts Institute of Technology 2 Computer Research Corporation NOTICES OCT 16 I Joint DCN News ItemsConference 2 Computer r oýb Approved by The Under 'Secretary of The Navy 27 August 1951 ----- - L THIS DOCUMEN BEST IS QUALITY AVAILABLE TIM COPY FURNISHED TO DTIC CONTAMND A SIGNIFICANT NUMBER OF TIS DOCUMENT CONTAINED REPRODUCED FROM BEST AVAILABLE COPY THAT HAVE BLANK PAGES BEEN DELETED NAVAL PROVING GROUND CALCULATORS During the past three months the Mark III Calculator and the Aiken Relay Calculator Mark I1 have continued to operate on a 24-hour per day schedule The operating efficiency of the Mark I continues at about 85 per cent That of the Mark III has shown a substantial improvement The average over the past four weeks was 82 per cent the most successful record for any similar period During this period an efficiency of 89 per cent was obtained for one week It is believed that improved preventive maintenance techniques and a more experienced operating staff are large factors contributing to the better performance Additional checking facilities have been designed by the Computer Research and Development Group for the Mark Iff Calculator and are now being installed Further refinements are in progress and will he installed from time to time in the near future In addition to the usual heavy program of ballistic computation performed on the Calculators during the past quarter a problem involving computatiors of Radar Cross Sections of a Prolate Spheroid was completed for the Willow Run Research Center the University of Michigan WHIRLWIND I During the period I December 1952 to I March 1953 a wutal of 781 programs exclusive of military applications were run Of interest among the scientific and engineering problems handled by the computer were 1 earth resistivity interpretations MIT geology and geophysics department 2 deuteron binding energy and wave functions MIT physics department 3 transient aerodynamic heating of a flat plate aero-elastic and structures laboratory 4 Lawley's method of factor analysis characteristic vectors modified educational testing service research department 5 optical properties of thin metal films MIT chemistry department A comprel nsive system of service routines using perforated paper tape as auxiliary storage has been in use durIng the above period of time However further development and refinement of this system continues In particular the system has now been modified to use two magnetic tape units as nuxiliary storage The use of the magnetic drum as further auxiliary storage is being studied These forms of auxiliary storage greatly reduce the amount of time taken by conversion In addition to the features discussed in the January 1953 Newsletter the comprehensive system now includes the automatic selection of output routines The programmer obtains the desired form of output by writing at the proper point of his program a sample number preceded by three letters which indicate essentially the output medium required typewriter punch magnetic tape or numeriscope A course is now being offered monthly to provide qualified persons with necessary training for programming on WWI In addition a seminar is being conducted for discussion of advanced programming techniques THE COMPUTER RESEARCH CORPORATION COMPUTERS CADAC 102-A odv ion CADAC 102-A is to be completed approximately 25 May 1953 Projd tron of M u ea iines has been initiated and by the summer of 1953 the production 9s duic wl e one C bAC 102-A completed every eight working days Two additions to the c---ic mahd lrtfave bee made since the October 1952 Newsletter eport '-2- 1 Alphabetic mode of print command enabling any character on the Flexowriter to be printed by programming the proper groups of six binary digits or two octal digits within the computer itself 2 A test search command enabling the computer to discover whether a magnetic tape unit is still searching or not This is a transfer of control command CRC 105 The first CRC 105 Decimal Digital Differential Analyzer has been delivered and the next three are in final test Various types of problems have been run on the first machine including interior ballistics research problems partial differential equation solution by net relaxation trajectory problems and a molecular crystal growth chemical problem CRC 107 The first two models of the CRC 107 are in final test and performance to date has been very good Experience with the engineering prototype magnetic tape unit indicates that high reliability will result from the use of double channel recording and the use of wide channels for reduction of dust and blemish troubles Twenty-two magnetic tape units are in various stages of production with the first production unit nearly complete MOORE SCHOOL AUTOMATIC COMPUTER MSAC Preliminary specifications for the MSAC power supply and power distribution system and for sources of one megacycle and eight megacycle sine waves have been completed as well as the schematics of the chassis for the main body of the MSAC Construction Is continuing on the timer unit and a small production line is being ucad to fabricate the pulse transformers for MSAC AIR FORCE MISSILE TEST CENTER COMPUTER FLAC The Florida Automatic Computer FLAC Fig 1 Patrick Air Force Base Florida is in the final stages of debugging The machine which has a word length of 44-binary digits plus sign operates with a floating three-address operation code i e the specified addresses may be either absolute or relative to either the program counter or special B register Operations it performs include addition subtraction multiplication rounded and unrounded highor low-order results available division remainder available complete decimal-binary and binary-decimal conversion logical transfer shift equality sensing comparison and file The present 512-word mercury-delay-line memory is capable of expansion to 4000 words with four 500-word-per-minute tape units providing external memory The external memory units operate with permanently recorded block marks for hunting as well as facilities for altering any block of data stored on an external memory tape Operating speeds and circuit philosophy resemble the Bureau of Standards SEAC However the machine employs only 380 tubes plus an additional 350 for each 512 words of acoustic-delay-line memory The machine employs seven basic plug-in assemblies which contain all circuit elements see Fig 2 Built-in refrigeration provides for parallel cooling of all components thus insuring long life and improved machine operation A comparison-type problem preparation unit and automatic format output printer designed around a Flexowritpr machine has been placed in operation The central control and inputoutput circuits for the computer are operational and debugging is progressing through the arithmetic unit and high-speed memory 3 IFI FL AC Fkirttda Aouisttintic Cmunipurr Pt tr ic Air Force iable0 Flolr'id Viewtt temoporary c-ontrol console to-mputter and wive inptl dunun r ii FLAG - F'lorida Autoniatic Computer Patrick Air Force Base Florida Plug-in package types - Left-to-lRight I Spare Diode Z Delay line - 16 - 1 4 11 sec sections 3 Delay Line Termination 4 Amplifier and Diode gating package -4- nvithgetic THE SEAC The three-address mode of operation whose circuitry was installed ard checked by coding and running a check routine and prime number routine is now available for regular operation on SEAC along with the four-address system A multi-channel tape drive and its associated circuitry have been completely checked out and the unit is operating as an integral part of the input-output equipment A magnetic wire dumper capable of both input and output operation has also been constructed and installed Engineering time during the past several months was devoted primarily to modifying the circuitry associated with the experimental Williams type memory and running evaluation tests Installation of the low voltage and efficiency of SEAC vOde a constaiit and regulated d-c power supplies and a-c regulators is underway to eliminate poor regulation which have been adversely affecting the over-all operating In addition a closed-circuit air cooling system is being installed to prosomewhat lower ambient tempcratu c within the k-U'inutel In order to establish a more systematic method for trouble-shooting such a complicated machine and to enable inexperienced technical personnel to isolate troubles more readily a number of new diagnostic test routines have been written and several of the old routines improved Reliable tests are now available for diagnostic checkinj of all parts of the machine including the Input-output units Average 'good operating time for the past six months of 1952 was slightly over 75 per cent of total assigned time for a 168-hour week good time being defined as time during whica problem solutions and code checking were turneo out correctly plus time during which the computer was in good operating condition but id This compares more than favorably with the 65 per cent figure for the previous quarter THE LAS COMPUTER From October 1952 through February 195 the LAS machine has been on an 80-hour week of which about 20 hours have been devoted to engineering and 10 to scheduled maintenance The machine is available for computation about 50 hours per week and operates error free about 64% of this time All calculations are done twice and exact duplication of results is required During this period a variety of problems have been solved or are current4y ' ng undertaken They include a large number of meteorolgical forecasts several hydrody armical calculations a number of astrophysical calculations some work on the determination of quantummechanical wave functions a mathematical application of biology and some determinations of the eigenvalues and associated functions of symmetric matrices Forty-channel IBM input-output equipment has been added to the machine replacing the teletype units previously used and a 514 reproducing punch has been associated with the machine for this purpose Twelve words of 40 binary digits each are stored on a card and are handled at 100 cards per minute A magnetic drum of 2000-word capacity is now under development THE SWAC The operating efficiency of the SWAC has continued to increase during the past few months At present useful computing averagcs between 65 per cent and 70 per cent of the total operating time scheduled maintenance and testing about 15 per cent adjustment and checking of the electrostatic memory 10-15 per eent and out-of-order maintenance about 5 per cent Work on the project of adding a magnetic drum memory to the SWAC continues The magnetic drum memory control circuits together with selection matrices for reading and writing have been built and checked out Construction of synchronizing circuits between the SWAC computer and the drum memory is underway -5 - Experimental work on a modified version of the Williams' type of electrostatic memory continues and initial results promise a substantial improvement both in read-around ratio and insensitivity to flaws During the last quarter over 600 hours of computation were performed on some twenty problems of widely varying type Descriptions of these problems and the progress toward their solution are available in the quarterly reports of Projects and Publications of the National Applied Mathematics Laboratories National Bureau of Standards MONROBOT The Monrchot Corporation is to take over all functions of the Electronic Research and Development Department as a subsidiary of the Monroe Calculating Machine Company Orange New Jersey Three MONROBOTS are now under construction one undergoing final tests prior to delivery to a deiense activity a second is being assembled for use as a demonstrator and to establish a calculating service and a third for another defense activity is under construction Magnetic aroums are einpioyeu for last-access memory perforated tape f additional slowaccess economical storage Results are printed at ten characters per second oij rolls of paper 8-1 2 wide tabulated as required The entire calculator occupies a metal desk-size cabinet with built-in air cooling facilities for the 700 tubes employea A simple manually operated keyboard is provided for thL initial programming and factor-inserting operation Programs and numbers-20 decimal digits in length with the decimal point in the middleare read in from perforated paper tape to the magnetic drum and results can be printed and punched In printing and in transferring to or from paper tape digits may be eliminated as desired on the left or right The MONROBOT is designed as an all-purpose calculator performing addition subtraction multiplication division comparison and automatic modification of orders Its power consumption is less than 3000 watts from a 110-volt AC line It weighs less than 2000 pounds The MONROBOT made its public debut on the night of November 4 1952 when it was moved into the Radio City New York television studios for use on the TV broadcast of the national election results over the NBC network THE CIRCLE COMPUTER Final assembly of the first production model of the Circle Computer was scheduled for completion early in April 1953 to be followed by debugging and reliability checking THE JACOBS INSTRUMENT COMPANY COMPUTERS JAINCOMPS Progress continues on the construction of JAINCOMP-C a high-speed real-time control computer of the all-parallel all-electronic JAINCOMP variety It has a basic addition time of 8 microseconds Its program is controlled by an electronically scanned' punched card from which any 3-address order can be read in I microsecond The machine has five different types of storage totaling 231 24 -digit words 5544 bits Access time for some types of storage is I microsecond for other types 4 microseconds Automatic checking facilities are included The entire computer complete with its multiplicity of input and output channels but exclusive of the punched-card holders fits in a cabinet 27-9 16 x 24-I18 x 22 in 8 5 cu ft This cabinet contains a forced-air cooling system All circuits are of the plug-in variety and are replaceable in thirty seconds Work has continued at a low level on the logical design of JAINCOMP-D an unusually versatile general-purpose computer which will be about 25 k larger than JAINCOMP-C Preliminary design studies have been made of JAINCOMP-type computers for real-time computation and simulation New components include a small magnetic amplifier weighing 0 007 oz and capable of putting out a 1 5-watt pulse of 5 microsecond duration very 25 microseconds a compl ely 6 potted 2 ' nit ir ec' ind del iy line weighing 0 63 oz and a shaft-position digitalizer capable of giving vt - hih 'ccUracy in a11gl Il e asuremelit in 0 1 milliecond or less Since the l • t Dit'ital Compolpr Newsletter release on the Consolidated Computer April 1 95' the desigin has been completed and construction has been progressing on the first instr nient By I March 1953 all commands were checked out on the laboratory text assembly of the arithmetic and control circuits On 9 March tests were begun oi the magneticdrum memory system which stores 4000 words of 10 decimal digits and sign and has also 80 words of quick-access memory After both sections are separately checked It is planned to couple them together to form an integrated computer on about 15 April Test and diagnostic routines subroutines and various problems are now being coded and placed on tape by the Machine Operation Section The prototype which will bt essentially the same as the laboratory test model but housed in a cabinet is under way concurrently and should be complete about May or June 1953 It is planned to retain this machine at Consolidated for application problems The input to these first two computers-the laboratory test model and the prototype-will be by means of photo-electrically read perforated paper tape Binary-coded decimal digits are read in at the rate of 450 or more digits per second OutpUt is to a tape punch with a speed of about 12 digits per second or directly to a Flexowriter at about 8 digits per second Development is under way on a coupling unit to permit use of IBM cards as the input-output medium THE ERA 1103 COMPUTER The Engineering Research Associates Division of Remington Rand Inc 1902 West Minnehaha Avenue St Paul W4 Minnesota has announced a new gene'ral-purpose computer system named the 1103 Details will beý published in a forthcomiing New sletter THE RAND t ORPORATION COMPUTER The Rand Corporation 1700 Main Street Santa Monica California is constructing for its own use a large general-puroose digital scientific computing machine patterned after the Princeton machine The main frame is completed and partially wired All registers adders digit resolvers and about one third of the control are constructed and tested A 10-digit prototype version of this machine capable of performing additions and right or left shifts is in operation In the near future a 128-word Selectron memory will be added to it for further tests The 256-word Selectron memory for the large machine will follow soon after Plans for a drum memory and for the console are completed Power supplies and refrigeration equipment will be installed and put into operation within a few months Arithmetic unit testing is sciteduled for late spring ABERDEEN PROVING GROUND COMPUTERS The following table gives a summary of the utilization of the three high-speed digital computers at the Ballistic Research Laboratories of the Aberdeen Proving Ground during the calendar year 1952 Figures for the ORDVAC and EDVAC cover the 39 weeks beginning 7April 1952 Engineering time is classified as scheduled or unscheduled Scheduled engineering is that time regularly scheduled in advance each week for servicing or engineering changes This includes the bad as well as the good test time used to determine if the machine is ready for -7- problem operation Unscheduled engineering is all other engineering t' the machine for problem operation and includes both good and bad tes' pare The total available time is divided into three parts Problem -king time includes also the good test time used to determine whether the n i r ood operating condition while these functions or a problem is in progress t tne spent in productive output Idle time is that in which the machine is knlo i iý i z good operating condition and is attended by a maintenance crew but not in use on problems Total machine time does not Include standby time when no attempt is made to operate or service Average Machine Week in Hours ORDVAC Scheduled Engineering Unscheduled Engineering Problem Set Up and Code Checking Production Idle Total Machine Time EDVAC ENIAC 23 8 27 2 39 1 29 4 26 3 34 4 70 4 23 3 21 7 2 4 12 5 35 6 20 4 67 1 3 7 145 8 152 2 139 3 ENIAC Ihe Burroughs Research Division has completed at Philadelphia a 100-word static magnetic-memory under Army Ordnance Corps commission for use with the ENIAC at the Ballistic Research Laboratories Aberdeen Proving f round Its speed is 50 000 ten-decimaldigit numbers per second DATA PROCESSING AND CONVERSION EQUIPMENT TELEDUCER Telecomputing Corporation 133 East Santa Anita Avenue Burbank California has developed the Teleducer a device which converts dc voltages into the corresponding digital representations The Teleducer reads out upon demand starting from a reset condition and ta-king 0 8 second or less to reach a balance Its digital output is then ava lable for recording Rs accuracy is 0 1% of full scale The three-decimal-digit output is in the form of contact closures Since it is a bridge-balancing device the input impedance at balance is essentially infinite ts maximum sensitivity is 20 microvolts per unit increment or 20 millivolts full scale The sensitivity is continuously variable down to I millivolt per unit increment SA DIC Consolidated Engineering Corporation's Type 33-102 SADIC Analogue-to-Digital Converter is a self-balancing Thompson-Varley potentiometer Its average balancing and conversion time is one second The full-scale input signal of 10 volts is divided into 1000 equal steps providing 0 1% accuracy SADIC's companion Type 1-121 Amplifier accepts positive or negative signals within the range of 1 to 64 millivolts with gain adjustable for full-scale output of 10 volts for such input signals Thus data-processing systems incorporating these units are capable of sensing and automatically digitizing a 1-microvolt change in an analogue signal The 3-digit numerical value is available both as contact closures and as a visual light display -8- BENSON iEHNER INCREMENTAL PLOTTER The Ben ion- l thner C trp•wration has annmunced its Incremental Plotter an accessory for the Computer Rescaccoh Corp'ora tion Model 05 Digital Computer which permits preparation of punched tilpes mid t iottln and rie ding curvs The lncronmental Plotter can plot a curve on an area 11 x 17 from a single tape input each sign il from• the pulsing unit advancing the plotter one increment 0 02 in in abscissa and advancing the tape revider one step The tape reading is then fed to the plotter as an increment in ordinate The plotter caii also operate from increments in both abscissa and ordinate specified by separate taipes at minimum rate of 10 pulses per second The device is capable of reproducing punched tapes and it can prepare tape or provide input to the computer from curves placed on the plotting table The pen carried on the intersection of the two crossbars is for this purpose repiaced by a photoelectric line follower The maximum permissible slope of the curve is 1 Output pulses are of 40-volt amplitude 4-microsecond duratior and less than 1-microsecond fall time In operating from the output of the computer it responds to pulses of 14 volts amplitude and 4 microsecond duration Benson-Lujner has also developed a Reversible Tape Reader which on command from the computer will advance or go back one step reading the tape to the computer positively or negatively respectively to provide increments in a dependent variable COLEMAN DIGITIZER The Coleman Engineering Company 6040 W Jefferson Blvd Los Angeles 16 California has developed the DIGITIZER a device for converting rotational shaft positions into electrical contact settings The DIGITIZER may be provided with lamp bank readout The same set of digitalizing contacts is used for a given lamp bank readout as is used for the corresponding automatic readout in order that there can be no hidden disparity between the signals observed at the light bank and the signals transmitted to the automatic recording system The contacts are separated from the brushes during rotation of the input shaft providing extraordinarily low torque-to-drive and virtual elimination of contact and brush wear The standard production models can be operated normally at upwards of 18 000 rpm at the units decade corresponding to 3000 digits per second Torque to start rotation of th linits decade input shaft is approximately 0 005 inch-ounces Retraction of the contact assembly is accomplished by suictnoid actuation The solenoid-energizing circuits may be either tied in with or independent of the drive system which positions the input shaft Standard production models are offered in three- four- and five-decade versions Six decades and over can also be furnished The four-decade model occupies an envelope measuring approximately 5 by 5 by 1-1 8 thick including contact-retracting solenoids The weight of this unit is slightly over two pounds FERRO-RESONANT FLIP-FLOP A smaller more rugged package requiring only 1 3 cubic inch for mounting space is featured in the new Model 133 Ferro-Resonant Flip-Flop recently announced by the Computer Research Corporation The new package has reduced the ferro-resonant flip-flop size by one-third and has reduced cost by fifty per cent It can deliver miore than 90ý of the input energy as usable output since copper and core loss are the only source of power consumption The use of non-dissipating reactive elements virtually eliminateý tht problem of heat dissipation Other features include operating at frequencies up to 100 k-- high power gain immunity to high acceleration and shock and the ability to withstand wide temperature humidity and pressure changes -9- _____ ___-_ ____ _ __ _ _ _ LOGRINC AUTOMATIC GRAPH FOLLOWERS The Logistics ReseaA ch Inc 141 South Pacific Avert ' Re uo teach California has developed two new autom'i' ýc graph followers The Logrinc Digital Graph Follower consists of a combination of the Digital Plotter and the necessary photo-electric and electronic components for automatically following curves and converting the data into electrical impulses The follower is suited as an input and output device for digital differential analyzers such as the CRC-105 or the MADDIPA-44A and may be used with either of these particular machines without additional equipment Working as an output device it will plot any two variables against one another each electrical impulse received causing an incremental movement of the pen As a follower it will handle any continuous function including those which have infinite slopes The drum holds paper sheets 12 x 18 inches The follower can follow the curve at a maximum rate exceeding 20 steps a second and deliver electrical impulses corresponding to incremental movemenis on both axes or it can allow motion on one axis to be externally controlled In this latter mode of operation incremental changes of 1 100 or 1 64 inches alung one axis are fed from an external source and the automatic follower produces electrical impulses to correspond with resulting motion on the other axis The electronics section of the follower is housed in a caster-mounted cabinet approxi¶rnately 30 inches wide 15 inches deep and 30 inches high The cabinet is designed to support the plotting drum at a convenient height For rapid preventive maintenance all electronic components are contained in plug-in units which are mounted on a swing-out chassis The Logistics Research Inc three-dimensional model has the same specifications as the standard Logrinc Automatic Digital Graph Follower except that It is designed to handle functions of two variables Families of curves on a single sheet may be placed on the drum and a separate externally controlled input will cause the follower to switch automatically from one curve to another This separate input or Z axis control is also incremental and bi-directional Incoming pulses will cause the iollower to change to an adjacent curve of the family in either direction Impulses corresponding to incremental movements in changing from one curve to the next are transmitted through the regular output channel -10- I 4 AVAILABILITY OF DIGITAL COMPUTING SERVICES Key a b c d Name and Address of Contact Facilities and their Location Coding and Mathematical Services To Whom Available 1 Purdue University a A 3 Perlis Department of Mathematics Purdue University Lafayette Indiana b Desk calculators IBM equipment including a CPC and complete auxiliary equipment A magnetic-drum digital computer is expected in late 1953 which will be located in the Statistical Laboratory at Purdue c Available d No restriction 2 Benson-Lehner Corporation a H 3 Rounds Jr Data Reduction Division Benson-Lehner Corp West Los Angeles 64 California b Equipment for analyzing oscillograms dial and ballistic film etc c Available d No restriction 3 Moore School of Electrical Engineering a Robert E Schultz Moore School of Electrical Engineering University of Pennsylvania 200 S 33rd Street Philadelphia 4 Pennsylvania b A Differential Analyzer a Card-Programmed-Calculator and desk calculators c Available d No restriction Preference given to proposals of a research nature 4 Computer Research Corporation a R E Sprague Computer Research Corporation 3348 W El Segundo Boulevard Hawthorne California b CADAC 102-A available after July or August 1953 c Available d No restriction -11- COMPUTER AND NUMERICAL ANALYSIS COURSES MASSACHUSETTS INSTITUTE OF TECHNOLOGY An intensive two-week summer program on computers and computer applications will be carried out under the direction of Professor Charles Adams assistant professor of digital computers who is in charge of general applications of the MIT Computer Laboratory The program will include an introduction to digital-computer coding and a survey of existing computers applications numerical methods and advanced programming techniques It will be supplemented by group discussions and by demonstrations and practice on the MIT Whirlwind I Computer COMPUTER RESEARCH CORPORATION Regular scheduled courses in programming and maintenance for general-purpose digital computers with emphasis on the CADAC 102-A will be offered at the Computer Research Corporation 3348 W El Segundo Boulevard Hawthorne California These courses will begin about May 1953 and will be offered approximately every two months Programming and maintenance courses will be conducted simultanec 'sly with one week of overlapping material It is expected that the course will last four or five weeks In addition at least one programming course on the CRC 105 will be given in the spring or summer of 1953 Inquiries on these courses should be directed to the CRC NOTICES DCN NEWS ITEM The Computer Branch of the Office of Naval Research Washington 25 D C solicits news items for inclusion in the Digital Computer Newsletter Material should be received by 10 March 10 June 10 September or 10 December for publication in the Newsletter of the following months JOINT COMPUTER CONFERENCE The annual joint computer conference sponsored by the Association for Computing Machinery Institute of Radio Engineers and American Institute of Electrical Engineers will be held this year in Washington D C at the Hotel Statler 16th K Streets N W on 8 9 and 10 December 1953 - 12-