The Commodore GL-979D calculator, introduced in 1975, is a member of Commodore’s Custom Green Line family. This arithmetic calculator offers 8-digit precision and operates on algebraic logic, making it a reliable tool for everyday calculations.
The calculator features a 7-digit VFD (vacuum fluorescent display), which provides a clear and bright image. The display is housed under an oversized green plastic filter that is flush with the case, giving the calculator a distinctive appearance. The Commodore logo and the words “Custom Green Line” are raised and painted silver.
The Commodore GL-979D is powered by two removable AA batteries, providing 3V DC. It also accepts an adapter (DC-420B, 2mm plug, center positive) through a socket on the right side, although the batteries must be removed first to avoid potential issues. The calculator’s case is a sturdy three-piece construction made of black and white matte plastic. The keys are bold red, white, and blue, each with its own raised surround. While the keys are somewhat wobbly and squishy, they function effectively. Below the keyboard, a black printed metallic sticker with the company name sits in its own recess.
Manufactured in Japan by Commodore Japan Ltd., the GL-979D measures approximately 75mm x 140mm x 28mm (width, height, depth) and weighs 128g excluding batteries. The calculator’s components include a Commodore GRBP-67 7540 CPU, an 8-digit single round tube VFD display, two transistors, six diodes, five capacitors, two SIL resistor arrays, four resistors, and one transformer. The keyboard board is fixed to the front with 10 screws and connected to the main CPU board with a 14-way ribbon cable.
The Commodore GL-979D offers standard four functions, percentages, reciprocal, square, register exchange, and one function memory.
Logic:
- (C) is used once to cancel the last number entered and a second time to clear the whole calculator.
- There is no constant on any functions.
- Input overflow is suppressed, inputting an eighth digit is ignored.
- Negative numbers are shown with a “-” in the immediate left hand digit , as there is no eighth digit you are limited to six digit negative numbers.
- The (M) key recalls the memory. To store in the memory just press equals twice – that’s why there is no constant function. Alternatively key in (3)(=)(M) to store three.
- Memory store is not indicated you have to remember it.
- It is possible to store an overflow in the memory and later recover it by continual division by 10.
- Divide by zero shows “E000000” (no decimal point) and is recoverable by dividing by one.
- Overflow shows the result with “E” (negative or positive) in the left most (seventh) digit and is recoverable by continual division by 10 or a multiple.
- (EX) is used to exchange the display with the last stored result.
- The (%) button divides by 100 so can be used to recover overflows.
The Commodore GL-979D is a robust and functional calculator with a unique design and a few extra functions compared to other members of the Custom Green Line series. Despite some oddities in its memory system and display limitations, it remains a reliable tool for basic arithmetic calculations.
