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Calculators: Desktop: Casio 121-MR
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Size (approx): | 120mm x
170mm x 32mm (max) (w,h,d) Weight 294g excluding batteries |
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Power: |
6V DC, 4 x AA size batteries, 0.35W. Does accept an adapter (AD-4145) through socket on the top side to the far left. | |
| Case: | Lower part of the case is matt and smooth dark grey plastic whilst the top consists of a cream section and a further black section. Painted metal keyboard surround in brown also holds the company name and model number. Keys are squashy and hollow sounding but work very well. Big calculator that only just fits in the hand and is more suited to the desktop. | |
| Display: | 12 digit blue VFD, no thirteenth digit. Red LED for minus indication. | |
| Features: | Standard four functions, percentages, square root, x/y, sign change and four function memory. Switches for count/sum, round up/down and fixed decimal point | |
| Age: | 1975 | |
| Manufacturer: | Casio Computer Co., Ltd. Made in Japan. Serial No. 5311660. | |
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Comments:
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Huge version of the familiar Casio shape and feel. Built to last – and be used every day and it has done. Originally (equally huge) case is soft black plastic with popper closing at the top. Lack of error recovery is a pain and inconsistent fixed decimal point takes some getting used to. |
| Components: | 1 x cpu: Hitachi HD3686 5M21
(2nd week of December 1975?) 42 pin DIL, 0.6" width 1 x 12 digit flat face single tube VFD display 6 x transistors 11 x diodes 9 x capacitors 2 x resistor arrays 15 x resistors 1 x transformer |
| Boards: | The main keyboard (Ref: B12L-E4 A) is attached to the front by four screws and houses the switches and LED. The main cpu board (Ref: B12L-1 A) is connected by 20 stiff copper connectors. A third small sub-assembly board houses the transformer circuitry. |
| Construction: | Remove the single screw in the battery compartment. From the bottom, slowly squeeze the white plastic to release the internal lugs. Hinge around the top as slowly as you can. |
| Logic comments: | (C) is used once to cancel the last number entered and (AC) to clear the whole calculator. |
| There is automatic constant on all four functions | |
| Input overflow is suppressed, inputting a thirteenth digit is ignored | |
| A red LED in the top left hand side of the display shows a negative sign and allows full thirteen digit negative numbers | |
| Divide by zero shows zero and is not recoverable | |
| Overflow shows the result and hooks the calculator up. It is not recoverable. | |
| You can have negative zeros. Try (2)(-)(3)(=) to give "-1" now (+)(1)(=) give "-0". | |
| Negative square roots will give you the answer but is not recoverable. | |
| There is no indication of memory – you have to remember it | |
| Even if you set the fixed decimal point switch to zero you still get full precision square roots |
