The Commodore GL-976M, also known as the GL-976MD, was manufactured by Commodore in Japan in 1975. This calculator is part of the Custom Green Line series, known for its distinctive design and functionality.
The manual for the Commodore GL-976M, and other Custom Green Line calculators, opened with a paragraph that stated: “Congratulations on your purchase of your new Portable Electronic Calculator. You have selected one of the finest, precision-built figuring instruments. A tiny, solid state chip of silicon, no bigger than this letter “M” contains the brainpower for your calculator. Engineers refer to this miracle of super miniature wizardry as, “Large Scale Integration,” (LSI). It is your assurance of optimum reliability and increased durability.”
The GL-976M features a sturdy, three-piece case constructed from black and white matte plastic. The top front of the calculator is adorned with an oversized green plastic display filter, which is flush with the case and has a sloping inset section. This design element not only enhances the aesthetic appeal but also provides a bright image, making the display easily readable. The Commodore logo, raised and painted silver, along with the words “Custom Green Line,” is prominently featured on the display filter. The keys are boldly colored in red, white, and blue, each with its own raised surround. While the keys are described as wobbly and squishy, they are functional and responsive. Below the keyboard, a black printed metallic sticker bearing the company name sits in its own recess, adding a touch of elegance to the overall design.
Powered by 3.0V DC, the GL-976M operates on two AA-size batteries. It also accepts an adaptor (DC 420B) through a socket located on the right side, just above the midway point. The calculator’s display is a 7-digit green Vacuum Fluorescent Display (VFD), notable for its clarity and brightness, although it lacks an eighth digit.
In terms of features, the GL-976M offers standard four functions with percentages and a multi-key memory system. The calculator’s logic is reliable, with good recovery from errors and no detectable bugs. The two-key memory system, while somewhat cumbersome, becomes easier to use with practice.
The calculator’s components include a Commodore GRBP-67 7536 CPU, a 9-digit VFD, two transistors, six diodes, five capacitors, two resistors, two resistor arrays, and one transformer. The main CPU board (GL-997R PCB NO.200752 Rev A) sits atop the keyboard assembly (SI 1676) and is secured with the adapter socket. A long 14-way ribbon cable connects the two, and the latter is fixed to the front with ten screws. The display power circuitry is situated on a mini board.
Opening the calculator for maintenance or repair is challenging due to the tight internal lugs on the sides. Removing the two screws from the back is straightforward, but further disassembly requires careful manipulation to avoid damage. A white side lug halfway between the bottom and the adapter socket must be pushed in while prying with a blunt wooden or plastic stick. Similar steps are needed on the side and top to fully open the calculator. Reassembling the device is equally tricky.
Logic:
- The (C) key clears the last entry of a number press; pressing it again clears the entire calculator.
- Overflow on number input is suppressed; typing an eight-digit number ignores the eighth digit.
- An overflow shows the result with an “E” in the left (seventh) digit and is recoverable by repeated division by ten or multiples.
- Divide by zero results in “E000000,” which is recoverable by dividing by 1.
- There is no constant on any function.
- Memory usage requires two key presses: (=)(M) to store, (+)(M) or (-)(M) to accumulate or decrement, and (0)(=)(M) to clear.
- There is no indication of memory usage; users must remember the stored values.
- Negative numbers are flagged by a “-” sign in the immediate left digit, limiting users to six-digit negative numbers due to the lack of an eighth digit.
- The percentage key divides by 100 repeatedly and can be used to recover overflows.
The Commodore GL-976M is a well-designed, basic calculator with a distinctive aesthetic and reliable functionality. Its bold, simple design and sturdy construction make it a notable example of mid-1970s calculator technology. Despite its basic features, the GL-976M offers a reliable and user-friendly experience.
