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Calculators: Handheld: APF M74
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Size (approx): | 72mm
x 135mm x 17-23mm (w,h,d) Weight 86g excluding batteries |
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Power: |
9.0V DC, 1 x PP3 size battery. It accepts an adapter (DC 9V model 751S, model APF 7510) through a socket on the left right side at the top. | ||
| Case: | Slightly wedge shaped case made from two-piece black matt plastic construction. The larger to area (to accommodate the battery) has a vertical ridged design. The red plastic display filter is tilted at about 20 degrees and fits flush to the case as well as wrapping around the side edges. It gives a deep set bright but limited angle of view image. A large brushed aluminium panels surrounds the keyboard and similarly warps around the edges. It is printed with black text for the key and switch labels along with the brand and model number. The original sticky plastic protector is still in place on my example. The keys are short travel with a loud click and work very well. | ||
| Display: | 8 digit red LED with bubble lens and no ninth digit | ||
| Features: | 4 function calculator with percentages, sign change and four function memory. | ||
| Age: | 1979 | ||
| Manufacturer: | APF Electronics Inc., New York, N.Y. 10022, USA. Made in Singapore. Serial number 492784 and a further reference number 0972 is shown on the back sticker. | ||
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Comments:
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Cheap and hollow calculator typical of the late LED era. Collectors guides refer to this as the Mark 74 but the documentation and box sticks with the model M74 label. Battery compartment is a bit too tight for the battery as is common. The logic is OK with good recovery (except for memory overflow) but is let down by seven digit negative numbers and the pseudo fixed decimal bug. It was not supplied with a case just a bubble-wrap bag. |
| Components: | 1 x CPU; Texas TMS0972NL MBT
7932 Singapore (week 32 of 1979), 28 pin DIL, 0.6" width 1 x 8 digit bubble lens red LED display (with a ninth bubble) |
| Boards: | The main cpu board (M74 TMS0972) sits lose above the keyboard assembly and is connected by a 15-way ribbon cable. The keyboard is attached to the front with nine screws. |
| Construction: | APF appear to have invented the first nanometer scale edge seal. Very very difficult to prize apart the two halves to pop the internal lugs. Be warned, damage is sure to result if you try. If you must, then then best way I found was to lever apart the bottom edge. I use plastic coffee cup stirrers (helpfully donated by coffee houses) as these are soft enough not to case damage. |
| Logic comments: | The (CE) button is used to clear last entry of a number and the (C) clears the whole calculator. |
| Overflow on number input is suppressed inputting a ninth digit is ignored | |
| Negative numbers are shown with a - to the immediate left of a number but as there is no ninth digit to travel into, you are limited to seven digit negative numbers. | |
| An overflow shows the result flashing which is recoverable using (CE) with no indication of error except that it hooks up and is not recoverable. | |
| Divide by zero shows a flashing 0. and is recoverable using (CE) | |
| The change sign function can be used in mid number entry | |
| There is automatic constant on all four functions | |
| There is no indication of memory store you have to remember it! | |
| An overflow in memory results in a flashing number and is not recoverable and clears the memory. | |
| It suffers the pseudo fixed decimal bug; key in (1)(+)(0)(.)(0)(0)(0)(=) and it shows 1.000 which remains a fixed three digit decimal number until exceeded by a four digit decimal point answer. |
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The box measures 78mm by 140mm and is 30mm deep so just about accommodates the calculator. It is printed in two-tone blue and is a reverse tuck-end construction. My particular sample has a catalogue number on it (L29 05 4477 7) which looks like a retailers sticker. Made in Singapore. |
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The manual doesn't even have a front cover as it
is a basic, black and white 8 page fan-fold leaflet. It measures 70mm
by 115mm. In English only it has basic instructions only.
Ref 0972, Singapore. Servicing under 12 month warranty at 43-17 Queens Street, Long Island City, NY 11101 and 47 Valley Brook Drive, Don Mills, Ont. Canada. It offers a ninety day warranty but... There is an additional thicker 12 month Warranty card stating international service centres. In the UK this is listed as R. Groves (Elec. Serv.) Ltd., Threaf House, Wallingford Road, Uxbridge Industrial Estate, Uxbridge, Middlesex.
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| Footnotes: | Bruce has kindly supplied the serial number of his example which is 468799 |
