Caltronic 812

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Calculators: Handheld: Caltronic 812

		Size (approx):	76mm x 146mm x 20-32mm (w,h,d) Weight 186g excluding batteries.
		Power:	9V DC, 1 x PP3 size battery. It accepts an adapter (undefined) through a socket on the top side to the far left. There is a display-fade power save function.
		Case:	Two piece case in matt black plastic with a wrap around side band of brushed aluminium. Below a ridged design the red plastic display filter sits deeply inset and tilted. It is convex to give added magnification. Below this is a black printed metal panel which sits in its own recess and contains the brand and model number in black dotted font text. Another recessed metal panel surrounds the Klixon keyboard with engraved switch labels. The keys are short travel with a loud click.
		Display:	8 digit red LED with a ninth digit for negative indication. Extra pinpoint LED for battery low power indicator.
		Features:	Four function with semi-RPN input. Switched 2/0 fixed decimal points.
		Age:	1972/3
		Manufacturer:	Caltronic, made in Hong Kong, serial number 41629.
		Comments:	Early bulky basic calculator with archaic functions but sturdily built. The logic is pants with limited decimals, strange 12 digit calculations and numerous bugs. The original black plastic cover is side-bottom-side zip case with Caltronic 812 embossed on the front. The inside is lined with purple felt with Caltronic 812 in framed silver – testament to the high price no doubt. It also has a black plastic, purple felt lines carry strap.

Components:	1 x cpu: Cal-Tex CT5002 7238 (week 38 of 1972), 40 pin DIL, 0.6" width white ceramic with metal cap 2 x IC Texas SB75492N 7244 (week 44 of 1972), 14 pin DIL, 0.3" width black plastic 1 x IC: RCA CA3081 E 237, 16 pin DIL, 0.3" width black plastic 3 x 3 digit LED units with individual bubble lens 4 x transistors 17 x diodes 12 capacitors 31 x resistors 1 x variable resistor
Boards:	The main cpu board (CT 52) sit face down and is held by two screws, which can then be removed from the display (DL-33) edge socket. The display board/keyboard assembly is held in by four screws, two of which hold a bracket over the 22x2 way display edge connector. The keyboard assembly (3 45227 2nd issue, Texas Instruments Inc IKS116) has the metal trim and switches as part of the integrated unit.
Construction:	Remove the four screws accessible from the rear of the calculator, the rear section then lifts off easily.

Logic comments:	The (CE) key is used to cancel an entry and (C) clears the whole calculator
	The logic is semi-Reverse Polish Notation: to do 6-2 key in (6)(+=)(2)(-=)
	Overflow on the input of a number is not of suppressed and weird: whilst the display is eight digits you can input up to 12 digits (but the two left hand side decimal points light up) and only when you input a thirteenth digit does it overflow and is not recoverable
	There is no constant on any function
	Negative numbers are flagged by a "-" sign in the far left (ninth) digit thereby allowing full eight (actually twelve) digit negative numbers
	Overflow shows the result with the first two left hand digits alight if under thirteen digits and you can carry on. If an overflow is greater than twelve digits then the display shows “0.0.0.0.0.0.0.0.” and is not recoverable
	A divide by zero shows just a blank display and is not recoverable
	You can switch between no decimal places and fixed two digit decimals only
	It suffers the negative zero bug: key in (1)(+=)(2)(-=) to give “-1” now (+=)(1) gives “-0”
	It also suffers the divide to minus zero bug
	There is a power save feature that after 30/45 seconds (my example was 40 seconds) the display will just show “H” in the far right (first) digit which is recovered by pressing the (+=) key
	There is a low battery indicator – a separate pinpoint red LED to the right of the display that lights to tell you – and drains the power even quicker!


Further evidence of the "no expense spared" feeling of this calculator is the inner purple felt lined cover with silver lettering - wow!	With the main cpu board removed you can see the Texas Klixon keyboard assembly the display board and the gold coated edge connector to the main board.
	The fully removable, double sided, main cpu board is crammed with components, typical of its early pocket calculator era. Note the large white ceramic IC, 44-way gold plated edge connector, tantalum bead capacitors, sturdy transistor - all signs of an expensive machine. The two outer holes on the left are for the board fixing screws, whilst the two inner ones fix the rear of the case.