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Calculators: Handheld: Rockwell the 20T
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Size (approx): | 75mm x
138mm x 16mm (w,h,d) Weight 92g excluding batteries |
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Power: |
4.5V DC, 3 x AAA size batteries. Does accept an adapter (undefined but 3mm plug, centre positive) through socket on the bottom side to the far left. | ||
| Case: | Super slim two-piece case in dark brown and beige matt plastic. There is a large aluminium panel surrounding the keyboard with recessed on/off switch and brown plastic escutcheon. Keys are typical of the Rockwell colour scheme but short travel with a load positive click. The brand name is painted on the plastic whilst the model number and "on direction" (quite worn on this example) is printed in dark brown on the metal panel. A neutral, flat and flush, wrap around display filter gives a nice bright display. | ||
| Display: | 8 digit blue VFD, with a ninth digit for memory indication | ||
| Features: | Standard four functions, percentages, sign change and four function memory. | ||
| Age: | 1977 | ||
| Manufacturer: | Rockwell International, Microelectronic Product Division, Anaheim, CA 92803, made in Hong Kong. Serial No. 27545 -017. | ||
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Comments:
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Nice slim hand held calculator that is well constructed. The logic is sound but somewhat let down by seven digit negative numbers and no square roots. Original case is soft brown plastic with open top. Very similar to the 18T which uses the same IC but with less functions available. |
| Components: | 1 x cpu: Square spiral design CF589
7710 (10th week of 1977), 28 pin DIL, 0.6" width black plastic 1 x 9 digit flat face single tube VFD display 2 x transistors 8 x diodes 5 x capacitors 2 x resistor arrays 6 x resistors 1 x transformer |
| Boards: | The main cpu board (Ref 38P750 1P2760 20T REVA SH2) is secured to the front by two plastic lugs and two screws. It is connected via 13-way ribbon cable to to the keyboard board which is fixed using 7 plastic rivets. The main board has a cut out to let one of the larger cylindrical capacitors sit half way through - and reduce the overall thickness. |
| Construction: | Tricky. From the reverse slowly separate the bottom and travel up one side pushing in the brown plastic to separate the (two) lugs. When complete do the other side and finally hinge off the top. |
| Logic comments: | (CE) is used once to cancel the last number entered and (C) to clear the whole calculator. |
| There is automatic constant on all four functions | |
| Input overflow is suppressed, inputting a ninth digit is ignored | |
| Negative numbers are shown with a "-" to the immediate left of the number, as this does not travel into the ninth digit it is limited to seven digit negative numbers. | |
| Using the change sign key assumes you have finished inputting the number as you cannot add further digits. | |
| Trying to input an eight digit negative number by (1)...(8)(+/-) causes an error display "C.-.1.2.3.4.5.6.7." which is recoverable using (CE) | |
| Divide by zero shows "C........0." and is recoverable using (CE) | |
| Overflow shows the result with "C" in the far left (ninth) digit and all decimal points alight. It is recoverable using (CE) | |
| Memory is indicated by the lower right hand segment in the far left (ninth) digit - the only time this digit is used. | |
| The memory is cleared by storing zero |
