Prinztronic 400

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Calculators: Handheld: Prinztronic 400 (aka M400)

		Size (approx):	74mm x 134mm x 22mm (max) (w,h,d) Weight 84g excluding batteries
		Power:	9V DC, 1 x PP3 size battery. It accepts an adapter (3V undefined) through socket on top side to the far right. The on/off switch is on the right hand side just above with the display.
		Case:	Wedge shaped with pronounced edges made from a black and grey two-piece matt plastic case. The red plastic display filter is slightly raised, tilted and flat. It gives a bright image but with limited angle of view. There is a poke-through plastic escutcheon, which is then surrounded by a large brushed aluminium plate, printed in black for the brand and model number. A similar plate surrounds the keys, printed blue and black. The keys are medium travel with a very pronounced click and have not survived well in my example.
		Display:	8 digit red LED with bubble lens and no ninth digit
		Features:	Standard four functions with percentage, change sign and four-function memory
		Age:	1978
		Manufacturer:	Made in Hong Kong, serial number A537505
		Comments:	Cheap and cheerful generic calculator that is not that well made. Other brand examples can be seen on Same Calculator page. The logic is quite good with good recovery and only let down by the pseudo fixed decimal bug.

Components:	1x cpu: Texas Instruments TMS0972 KBTP 7818 (date code week 18 of 1978), 28 pin DIL, 0.6" width black plastic 1 x 8 digit red LED unit with individual bubble lens: National Semiconductor NSA1488 836 no other components
Boards:	The main cpu board (M880 REV0 REVO 0972 101077) sits loose in the front of the case and is connected to the keyboard assembly via 12 strong wires.
Construction:	The case is held together with internal lugs only so be very careful not cause damage it if you want to open it. The best way I found was to approach one of the side edges, push in the light grey plastic sections and use a non-damaging implement (such as a plastic coffee stirrer) to prize up the black section. The back will eventually lift off, hinging from the bottom.

Logic comments:	(CE) is used to cancel the last number entered and (C) to clear the whole calculator.
	Input overflow is suppressed, keying in a ninth digit is ignored
	Negative numbers are represented by a “-“ in the immediate left hand digit but as there is no ninth digit you can only have seven digit negative numbers.
	There is automatic constant on all four functions
	Overflow shows the result flashing and is recoverable using (CE), if the answer was negative, you lose the least significant number
	Divide by zero shows zero flashing and is recoverable using (CE)
	The change sign (CS) can be used in mid number entry
	Memory store is not indicated by – you have to remember it
	It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to give “1.000” which remains a three digit fixed decimal number until more are required or you use multiply or divide
	(CA) appear to be a clear all key – even the memory is cleared