Busicom Colex 812-SL

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Calculators: Handheld: Busicom (Colex) 812-SL

	Size (approx):	77mm x 143mm x 17mm (w,h,d) Weight 172g including internal batteries
	Power:	4.8V internal rechargeable batteries 0.45W (4 x N sized 1.2V Matsushita batteries). It accepts an adapter/charger (model 24008 DC 6V 150mA) through a socket on the top side to the far right. A warning note tells you to switch the calculator off whilst charging and not to exceed 24 hours of charging.
	Case:	Very slim brick-shaped case of two-piece white smooth plastic. The true make of the calculator is shown by orange printed text above the display, but there is an additional metallic sticker with the Busicom brand. An inlayed black plastic line surrounds all the functional area, which is strangely to one side. The green plastic display filter is flat and flush. A metallic black printed sticker surrounds the top keys and on/off switch. The keys are very like some Commodore scientific models with inset printed labels in silver and black. The keys are soft and springy.
	Display:	8 digit green VFD with a ninth digit for negative and error and memory indicators
	Features:	Standard four functions with percentages, square root and five-function memory.
	Age:	1975
	Manufacturer:	Colex, made in Hong Kong, serial number H000617 (see further information below).
	Comments:	Gorgeous calculator with a stunning design and colour scheme. The logic is OK but the constant function is not as useful as usual and there is a strange divide by zero bug. This branded Colex machine is typical of later Busicom models that were imported and "badged". All other items like the box and manual are plain Colex brand. It makes you wonder how official this was, especially as the adapter is not quite right for the UK and looks like a grey import. There was a model 812 which appears in more pedestrian case, uses four disposable AA batteries and only had eight digits. Perhaps the SL stands for slim-line as the 812 looks quite bulky. The original cover is black shiny plastic with an open top and half-moon cut-outs on the front and back. It has Colex embossed on the front. Similar functions and insides to the Colex 812-R.

Components:	1 x cpu; Mostek MK50311N 7512 HHH, 28 pin DIL, 0.6" width 1 x 9 digit VFD single unit flat faced; Futaba 9-ST-12 5C (March 1975) 2 x transistors 8 x diodes 5 x capacitors 6 x resistors 2 x resistor array 1 x transformer
Boards:	The main cpu board (Colex 812SL-1) sits loose on top of the keyboard assembly (Colex KE-812 SL-U-1 B) and joined by 17 wires. The latter being held to the front of the case by 7 screws.
Construction:	Remove the two lower feet and undo the two screws you find underneath them. The back will gently lift off - hinging from the top.

Logic comments:	(C) clears the last number entered whilst a second press clears the whole calculator
	Input overflow is not suppressed, inputting a ninth digit results in an error, which is recoverable using (C)
	Negative numbers are shown with a minus to the immediate left of the number travelling into the far left (ninth) digit thereby allowing full eight digit negative numbers
	There is automatic constant on all four functions which does not default to the first register
	The change sign function can be used in mid number entry
	Divide by zero shows zero flashing” in the far left (ninth) digit and is recoverable using (C) which then appears to create a bug, where the next number entered becomes a decimal and goodness knows what equals does!
	Overflow shows the result flashing and is recoverable using (C)
	Negative square roots are not allowed and show the negative result flashing which is recoverable using (C)
	Memory store is shown with a small "L" in the far left (ninth) digit
	The percentage key just divides by 100, once


The adapter/charge was contained in the main box with its own separate red and green box. Measuring approx. 75mm by 57mm and 45mm deep. Oddly enough the adapter is a two-pin (shaver type) mains plug. My example came with a three pin adapter but I'm not sure this was standard issue as it does not fit in the main box easily. Model 24008, input 240V 50/60Hz, output 6V DC 150 Ma[sic].	The black and white manual measures 79mm by136mm and is 20 pages, in English only. It covers not only the 812-SL but the sister calculator; the 812. It consists of a good key description and plenty of examples. There is no origin information or reference number and it is a pure Colex manual only.	The back of the calculator has this sticker, as well as the metallic plate sticker from Colex. Broughtons of Bristol was obviously the importer for the UK for Busicom but I wonder how much they had to do with the branding when it arrived in the UK. Did they also stick on the front Busicom sticker? The complete lack of any other Busicom branding causes me to suspect that this was a very poor process and may even have been unauthorised!

		The main box measures 230mm by 115mm and is 60mm deep with a front opening construction. It contains an expanded polystyrene former that holds the calculator (not in its case). There is sufficient room for the boxed adapter with a remaining gap that is not quite big enough for the three-pin mains adapter with my example. Printed in black and red it has a panel at one end which has a stamped model number and serial number. Made in Hong Kong, no reference to Busicom.