The **Casio Memory-8F**, also known as the H-812, was a handheld calculator introduced by Casio Computer Co. Ltd. in 1976. Measuring 76mm x 138mm x 22mm (w,h,d) and weighing 128g including batteries, this calculator featured a sturdy, three-piece gloss plastic case with a black base, white top, and a matt black front panel. The display was an 8-digit blue vacuum fluorescent display (VFD) with no ninth digit.

The Memory-8F operated on 3.0V DC power supplied by two AA size batteries, with an option to use an AD-2S adaptor (3V centre negative) through a socket on the top side. The on/off switch was located on the left-hand side in line with the Casio branding.

In terms of functionality, the Memory-8F offered standard four arithmetic operations (addition, subtraction, multiplication, division) with percentages, square root, and a three-function memory. It had a switched floating or two-digit decimal mode, and users could enable automatic constant calculation for multiply and divide operations by double-hitting the operator.

The calculator’s components included an NEC μPD977C R63129 CPU, a single-tube VFD display (E6535A 6D), two transistors, five diodes, eight capacitors, four resistors, two resistor arrays, and a TDK transformer (4D CD1010). The main board (C8U-1A) was connected by 12 copper wires to the keyboard assembly (C8T-E4A), which was secured to the front panel with six screws. A small piggy-back board module housed the transformer and associated components.

Logic:

- The (C) key cleared the last entry, while (AC) cleared the entire calculator.
- Overflow on number input was suppressed, and keying in a ninth digit was ignored.
- Automatic constant mode was available for multiplication and division by double-hitting the operator.
- An overflow error was flagged with an “E” in the ninth (rightmost) digit, and was not recoverable.
- Divide by zero also showed an “E” in the ninth digit and was not recoverable.
- Mark up or mark down operations were performed with a single key operation.
- A round off switch and fixed two-decimal point notation were available.
- Square roots of negative numbers were allowed, resulting in a negative number.
- Square roots were limited to seven-digit precision.
- Negative numbers were flagged by a “-” sign in the immediate left digit, limiting to seven-digit negative numbers.
- There was no indication of memory store, and (AC) cleared the memory.
- Memory overflow cleared the memory, and recovery required (AC).
- The calculator suffered from the divide to negative zero bug and the negative zero bug.

The Casio Memory-8F was a robust and feature-rich calculator for its time, offering standard arithmetic operations, memory functions, and additional features like percentages and square roots. However, its logic had limitations, including issues with negative numbers, divide by zero, and memory handling.