Texas SR-10

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Calculators: Handheld: Texas Instruments SR-10 (type II) (aka Electronic Slide Rule Calculator)

		Size (approx):	77mm (max) x 160mm x 38mm (max) (w,h,d) Weight 200g excluding batteries.
		Power:	4.5V DC using 3 x AA size batteries. Also accepts adapter/charger (undefined but centre negative) through a top side socket on the left. Access to the battery compartment is by removing the rear half of the case.
		Case:	Bulky case made from two-piece glossy finish black plastic which is heavily wedge shaped. The top display area has a large silver painted trim and branding that tends to wear off easily. Within this is the on/off switch with embossed "on" label. A very steeply inset and tilted red plastic filter is well shielded from stray light. The keyboard surround is buff-coloured glossy plastic embossed with the model number. The large keys are very short travel with a prominent click. The rear has a practically full length instruction sticker.
		Display:	8+2 digit red LED display (flat multi-dot type) - with extra two digits for minus and error indication
		Features:	Basic four function with reciprocal, squares, square root and change sign. Scientific display with exponent.
		Age:	1974
		Manufacturer:	Made in Italy by Texas Instruments, serial number 040186
		Comments:	Bulky and solid feeling calculator with large easy to use keys that is more suited to the desktop but can just be used as a hand-held. However, it is rather ugly. The logic is quite good but odd with a roll-over exponent and continuation after error methodology. The original case is soft black plastic shaped in a matching wedge with flip over top flap and front popper closing. There were several versions of this calculator spanning from 1972 to 1974, this is the European type II.

Components:	1 x cpu Texas TMS0120NC C7341 (week 41 1973), 28 pin DIL, 0.6" width black plastic 2 x IC: Texas SN75493N 7347, (4 segment drivers) 16 pin DIL, 0.3" width black plastic 2 x IC: Texas SN75494N 7350, (6 digit drivers) 16 pin DIL, 0.3" width black plastic 12 x 1 digit red LED display 9 x transistors 14 x diodes 7 x capacitors 29 x resistors 1 x transformer One extra resistor and diode sits across the power socket to protect against reverse polarity
Boards:	The main cpu board (CP 2000331 REV D) sits face up on top of the keyboard assembly and is held in place by four screws. 14 short strong wires join the two together. The display sits on its own mini-board.
Construction:	Remove the two screws at the rear and the back lifts off easily, hinging towards the right so as not to stress the battery connectors. In fact you need to open the calculator up like this to change the batteries.

Logic comments:	The (CD) key is used to clear the last number inputted whilst the (C) key completely resets the calculator
	Overflow on input is suppressed: keying in a ninth digit is ignored
	There is no constant function
	The negative sign is shown in the far left (ninth) digit thereby allowing full eight digit negative numbers
	Overflow shows the result and "C" (or "E" if negative) in the far left (ninth) digit but you can just carry on calculating
	Divide by zero shows "C" in the far left (ninth) digit and you can carry on calculating
	The change sign function can be used in mid-number entry and before
	Square roots of negative numbers result in an error but show the result and you can carry on calculating
	Dividing 1 x 10^-99 by 10 just carries on with the exponent reset to zero and the error flag "C" in the far left (ninth) digit
	No major bugs found

This image shows the rear section of the case removed, exposing the main cpu board.

One main CPU and three additional logic ICs are typical of it's early date, as is the high component count and sturdy construction.

The smaller ICs either side of the larger CPU are display drivers.