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Calculators: Handheld: Commodore SR4912

Size (approx):

80mm x 147mm x 20-40mm  (w,h,d)
Weight 124g excluding batteries

Power: 9V DC, 1 x PP3 size battery. It accepts an adapter/charger (centre positive) located on the top side in the middle. Use adapter DC-505, 707, 708 or 709.  There is a power save function that switches the display off.
Case: Two-piece stippled black plastic case with silver printed trim. Raised brand name is also printed silver and has survived well on this example.  Keys in light and dark grey, white and black and a black keyboard surround.  The keys are short travel squishy type but work very well.   Heavily inset and tilted red display filter works quite well giving a large bright display.
Display: 8+2 digit red LED with bubble lens with a ninth digit for negative, error indications and an intervening digit for negative exponents.  The latter are the same size as the mantissa digits.
Features: Four functions plus percentages, change sign, brackets, reciprocal, pi, register exchange, square root, squares, nth root, logs, trigs, stats, polar coordinates, degree, radian , gradians and five function 9 store memory.
Age: 1978
Manufacturer: Commodore.  Made in Hong Kong serial No. 90899 with another number 201450-04
Comments: Workman like scientific calculator built to last. With 49 keys is this a button monster or what?  The SR prefix of this period indicates Slide Rule (or their name for scientific).  The "49" may refer to the number of keys, the 12 for the number of digits (pushing it!)  and they have dropped the "D" for disposable battery version. Considering its sophisticated functions it is odd that there are no constants, a memory store bug and no error recovery.

Components: 1 x cpu: MOS (logo) MPS 7561 005 3478 (week code 34 of 1978) 28 pin DIL, 0.6" width.
1 x LED with bubble lens display module
no other components
Boards: One board doubles as the keyboard and main cpu board (PCB No. 201478 Rev A) and is fixed to the front by six screws.
Construction: Remove the two long screws from the rear and the back section lifts off easily, hinging from the bottom.

Logic comments: (C/CE) is used to cancel the last number entered and a second time to clear the whole calculator.
There is no constant
Input overflow is suppressed, inputting a ninth digit is ignored
Negative numbers are shown with a "-" in the far left (ninth) digit thereby allowing full eight-digit negative numbers
Divide by zero shows "E" in the eight digit and is not recoverable
Overflow shows no number with "E" in the left (eighth) digit and is not recoverable
Negative square roots show no result and "E" in the left (eighth) digit and is not recoverable  
The change sign can be used in mid-number entry
Memory store is not indicated; you have to remember it.  To store in memory four use (STO)(4) and (RCL(4) to recall it.
It is possible to store an error state and confuse the memory; try entering 9 x 10 99  (STO)(1) then (M+)(1).  You get an error state but after using (C/CE) the number in memory-1 is corrupt.
There is a power save function; after about 60 seconds the display goes to a single (first digit) decimal point (except in th error condition where nothing is displayed).  Operation can continue by just pressing the next key you want - unlike the manual instructions (see below).
The (F) or function key is used to select the operation in the upper label
The (XCH) key is used to exchange the chosen memory register whilst the (X<>Y) key is used to exchange the calculator's registers
There is a power save function - after about 30 seconds just once decimal point will stay alight, pressing any key will continue.
The fare left (ninth) digit decimal point reminds you of gradian mode and the far right (first exponent) similarly for radians.


The box to the left measures approx. 87mm x 155mm and is 47mm deep, so not much else than the calculator went in.  It is printed in red, blue, black and silver so no expense spared.  The sides have French and German text and it is printed in Hong Kong.

Calling this a twelve digit calculator is rather pushing it.  Eight digit mantissa and 2 digit exponent yes, but the other two digits are used for the minus signs - cheeky!