Casio Mini CM-603

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Calculators: Handheld: Casio Mini (aka CM-603A)

	Size (approx):	153mm x 81mm x 37mm (w,h,d) Weight 236g excluding batteries, 242g including carry strap
	Power:	6V DC, 4 x AA size batteries. It accepts an adapter (AD-4145, 540mW) through a socket on the top side at the far left. The battery compartment has a red ribbon pull to aid removal.
	Case:	Horizontal format two-piece case in black textured plastic. The top and bottom edge have wrap around metal plates that give it a very solid feel. The slightly inset and flat neutral display filter has a printed white border. Below sits a black printed metallic sticker in its own recess. The large, long travel hollow sounding keys work well. The rear information sticker is upside-down. There is a swivelling metal post on the right side near the top for the black plastic carry strap.
	Display:	6 digit blue VFD, with no seventh digit but a display shift key to display up to 12 digits, small zero notation (see below).
	Features:	4 function calculator with display shift for 12 digit precision.
	Age:	1973
	Manufacturer:	Casio Computer Company Ltd. Made in Japan, serial No. 5112004 (on battery cover) and 4036113 inside.
	Comments:	One of a range of early, solidly built horizontal calculators by Casio. This one is probably the most basic with six digits and the early and short-lived shift key. Logic is pretty shaky with no recovery, dodgy minus sign and rubbish display. Not difficult to guess by the very large component count and early date codes this is one of the first Casio pocket-sized calculators.

Components:	On the CPU board: 1 x cpu: NEC µPD177C K38026, 28 pin DIL, 0.6" width 1 x IC: NEC µPD129C K37275, 16 pin DIL, 0.3" width 1 x 6 digit VFD; single tube round face, NEC LD8084 2 x diodes 2 x capacitors 2 x resistors 3 x resistor arrays On the power/display driver board: 6 x transistors 6 x diodes 14 x capacitors 14 x resistors 1 x transformer
Boards:	The main cpu board (9X1 6K-1A) holds the keyboard assembly. Underneath sits a power board (Fuji MDP-0610 A6591) is of nearly the same size connected via 12 strong wires.
Construction:	Remove the two screws, one at each side end, and the front lifts off easily. Or the back if you like as the whole calculator assembly floats free.

Logic comments:	The (C) button is used to clear last entry of a number and a second press (or the sequence (=)(C) ) clears the whole calculator
	Overflow on number input is suppressed, typing in a seven digit number ignores the seventh digit
	An overflow shows the result and hooks up the calculator except for the display shift function and is not recoverable
	Divide by zero shows all zeros with the decimal point half alight and is not recoverable
	There is no constant on any function
	Negative numbers are shown with a "-" in the digit to the immediate left of the number so you are limited to five digit negative numbers. However, you can see a result up to twelve digits by using the shift key but the negative sign disappears.
	The shift key (>), called the "Full Register Viewing Key" by Casio, shows you the least significant six digits for the product or quotient of your calculation.
	It suffers the negative zero bug: key in (1)(-)(2)(=) to give "-1" now add one (+)(1)(=) to give "-0"
	It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) which gives "1.000" which will remain a fixed three decimal digit number until more are required or you use another operation

	Note the unusual way that zero is represented - by only using the lower half of the digit (representative image).
	With the front panel off you can clearly see the main cpu board. The power board sits underneath separated by a sticky piece of stiff card. Most of the components are on the second board which is nearly the same size. Notice the VFD tube sits in its own cut-out to try and reduce the thickness. Compare in a window with the Casio CM-602.