Casio Mini CM-603

The Casio Mini CM-603 was a handheld calculator introduced in 1973 by Casio Computer Company Ltd. It featured a horizontal format two-piece case in black textured plastic with wraparound metal plates on the top and bottom edges, giving it a solid feel. The slightly inset and flat neutral display filter had a printed white border, with a black printed metallic sticker below it.

The calculator measured approximately 153mm x 81mm x 37mm (width, height, depth) and weighed 236g without batteries or 242g with the included carry strap. It was powered by four AA batteries or an optional AC adapter (AD-4145, 540mW) through a socket on the top side.

The display was a 6-digit blue vacuum fluorescent display (VFD) with no seventh digit, but a display shift key allowed for displaying up to 12 digits. It featured a unique way of representing zero by only using the lower half of the digit.

The calculator was a basic 4-function model with display shift for 12-digit precision. The large, long travel hollow-sounding keys worked well, and the rear information sticker was upside-down.

On the main CPU board (9X1 6K-1A), the calculator had a NEC μPD177C K38026 28-pin DIL CPU, a NEC μPD129C K37275 16-pin DIL IC, the 6-digit VFD tube, diodes, capacitors, resistors, and resistor arrays. The power/display driver board (Fuji MDP-0610 A6591) housed transistors, diodes, capacitors, resistors, and a transformer.


  • The (C) button cleared the last entry, and a second press or (=)(C) cleared the entire calculator.
  • Overflow on number input suppressed the seventh digit.
  • An overflow showed the result and hooked up the calculator, except for the display shift function, and was not recoverable.
  • Divide by zero showed all zeros with the decimal point half alight and was not recoverable.
  • There was no constant on any function.
  • Negative numbers were shown with a “-” in the digit to the immediate left of the number, limiting negative numbers to five digits. However, the shift key allowed seeing results up to twelve digits, but the negative sign disappeared.
  • The shift key (>), called the “Full Register Viewing Key,” showed the least significant six digits for the product or quotient.
  • It suffered from the negative zero bug and the pseudo fixed decimal bug.

The Casio Mini CM-603 was a solidly built, horizontal calculator with a unique display and early components, but limited functionality and logic issues typical of early pocket calculators.

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