The Commodore GL-997R calculator, released in 1975 by Commodore Business Machines, is part of the Custom Green Line series. It balances functionality with a distinctive aesthetic, reflecting Commodore’s transition from office machinery to consumer-oriented devices. Manufactured in both the UK and Japan, the GL-997R was marketed as a reliable tool for business and personal use, leveraging Commodore’s reputation for durable hardware in an era when portable calculators were still emerging as staples of everyday use.
Physically, the GL-997R is compact, measuring approximately 75mm in width, 140mm in height, and 28mm in depth, with a weight of 172 grams including batteries. Its three-piece case, constructed from sturdy matte black and white plastic, features a sloping green display filter on the front top panel. This filter, embossed with the silver Commodore logo and “Custom Green Line” text, frames an eight-digit green vacuum fluorescent display (VFD) with a ninth digit reserved for memory, negative, and error indicators.
The keyboard, adorned with bold red, white, and blue keys set in raised surrounds, offers a tactile—if slightly wobbly—experience. Below the keys, a recessed metallic sticker displays the company name. Surviving units often exhibit yellowing of the originally white plastic casing.
Power is supplied by two internal AA-size rechargeable batteries. A 3V DC adapter (models 996R or 997R) can be connected via a 2mm center-positive socket on the right side. Internally, the GL-997R houses a Commodore GRBP-89 7531 CPU, dated to week 31 of 1975, alongside a single nine-digit VFD tube, discrete transistors, diodes, capacitors, and resistor arrays. The keyboard board (KB-6237-12 HM-24-10-RCB) is affixed with 11 screws and linked to the main CPU board (PCB200432 ART-200433 Rev-A) via a 14-way ribbon cable. Disassembly requires removing two rear screws, gently separating the case halves, and loosening the adapter socket to access the main board.
Logic
- The (C) key cancels the last entered number on the first press and clears the entire calculation on the second.
- Automatic constants are applied to all four arithmetic functions.
- Input overflow is suppressed; entering a ninth digit is ignored.
- Negative numbers display a “-” in the ninth digit, allowing eight-digit negative values.
- The (MT) key transfers memory contents to the display and clears the memory.
- Memory storage is indicated by a decimal point in the ninth digit.
- Division by zero triggers “E00000000” (no decimal point), recoverable by dividing by 1.
- Overflow displays an “E” in the ninth digit (positive or negative) and can be resolved through repeated division by 10 or multiples.
- The (EX) key exchanges the display with the last stored initial value (e.g., after 5 × 6 = 30, pressing EX recalls 5).
- The (%) key divides by 100, enabling overflow recovery.
The GL-997R combines quality construction with a logically structured interface, albeit with quirks like its two-stage clear function and memory management. Its design prioritizes clarity through the bright VFD and color-coded keys, while the reliance on rechargeable batteries and adapter compatibility reflects early efforts toward user convenience. Though overshadowed by later models, the GL-997R is a great example of 1970s calculator innovation, bridging mechanical reliability with emerging digital practicality.
