Microlith X

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Calculators: Handheld: Microlith Unknown model number (suspect 111)

		Size (approx):	70mm x 132mm x 15-22mm (w,h,d) Weight 100g excluding batteries
		Power:	9.0V DC, 1 x PP3 size battery. It accepts adapter (undefined) through a socket on the top side to the far left.
		Case:	Two-piece matt black plastic case with a prominent ridged design at the top. Below this is a full-width glossy black plastic panel with a silver printed brand. The red plastic display filter is heavily inset and tilted to give a reasonable if limited angle display. The sloping keyboard area has a inset brushed aluminium panel with black printed switch labels. The small keys are short travel with a strong click action.
		Display:	8 digit red LED with individual bubble lens and a ninth digit for negative indication.
		Features:	4 standard functions with percentages and register exchange.
		Age:	1975
		Manufacturer:	No details as the back label is missing on my example.
		Comments:	Can anyone help with the model number for this calculator? From the board I suspect that this was a model 111 or 113, but it does not match others on the web. Lightweight calculator with simple functionality. The logic is fine except for the pseudo fixed decimal bug. The original case is shaped soft black plastic with open top and half-moon cut-outs either side.

Components:	1 x IC: Unmarked U111 7540 (week 40 of 1975), 40 pin DIL, 0.6" width 1 x 9 digit LED module with individual bubble lens: Optostic 243 2875 2 x transistors 2 x diodes 3 x capacitors 6 x resistors 1 x transformer
Boards:	The main cpu board (750708C Microlith 111.113) sits face down on the keyboard assembly (ETCO A/W 145071 REV B) and is connected through 11 very short wires and one flying wire. The main board has lots of spare holes so is likely to be generic to a number of models.
Construction:	Held together by internal lugs only, the case can be separated by levering out the rear edge. The back will come away.

Logic comments:	(C/CE) cancels the last number entered whilst (C) clears the whole calculator
	Input overflow is suppressed; inputting a ninth digit is ignored
	There is automatic constant on all four functions
	Negative numbers are represented by a "-" sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
	The (<->) key exchanges the current with last register
	Overflow shows the result with all seven decimal points alight and is recoverable using (C/CE) when the shifted answer is displayed
	Divide by zero results "0.0.0.0.0.0.0." and is recoverable using (CE/C)
	This calculator suffers the pseudo fixed decimal bug; try entering (0)(.)(0)(0)(0)(+)(1)(=) to give "1.000" which remains a three digit decimal number until more digits are required or you use multiply or divide