Commodore Minuteman 3 Metric type II

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Calculators: Handheld: Commodore Minuteman 3 Metric (type II)

		Size (approx):	75mm (max) x 105mm x 27mm (max) (w,h,d) Weight 156g including batteries
		Power:	6.0V DC, internal rechargeable battery. Accepts an adapter/charger (6V DC 200mA, 3.5mm centre positive) through top side socket in the middle. An extra green sticky label is on the back of my example stating "If display does not light after adaptor is plugged in, turn machine off. Allow batteries to charge over night." There is a power save function when the display switches to a central "-" after about 20 seconds.
		Case:	Lovely palm-sized beige and brown matt two-piece plastic calculator. The upper area is dominated by a black painted metallic panel which is silver printed with switch label and raised Commodore logo. A red, slightly tilted and raised plastic display filter gives a bright but limited viewing angle image. The keyboard is surrounded by a black plastic panel. The keys are squishy but positive enough. Sticking with the red white and blue key colour scheme this compact calculator just oozes quality. In this example the conversions are listed as white printed key labels.
		Display:	8 digit LED with bubble lens and ninth digit for minus and overflow indication
		Features:	Four function plus percentages, two function memory and conversion functions.
		Age:	1974
		Manufacturer:	Made in England. Serial No. 031962
		Comments:	The minuteman series was a great concept for sturdy handheld calculators. Though most had a flat LED display this model has the more limited bubble lens type. The (CE) key acts as a function key (Conversion Entry) to change the operation of a number of keys - very confusing. The rest of the logic is poor, let done by the negative zero bug and a confusing memory system. Would it be a little cynical of me to suggest that this was a good way of saving money by not having a custom key labelled (CONV) perhaps? Original case is stiff brown plastic with flip over top and popper closing. The rear label has the item "Imperial" on it so there must have been a US version as well. Very similar to another Minuteman 3 Metric (type I).

Components:	1 x cpu: MOS MCS 2521A006 1374 (date code week 13 of 1974), 26 pin DIL, 0.6" width light grey ceramic, in its own socket 2 x chips: One ITT 491 7310 (week 10 of 1973) and one ITT 492 7442 (week 42 of 1974) display drivers both 14 pin DIL, 0.3" width 1 x nine digit red LED display 1 x transistor 3 x diodes 3 x resistors (one joined between the battery pack and adapter socket) 5 x capacitors 1 x transformer: Sumida Japan
Boards:	Main CPU board is is soldered to the keyboard assembly underneath by 13 wires. It has the reference numbers PCB 300348, ART 300349B, ASSY 300350. A 17-way ribbon connector joins to the display.
Construction:	Remove the two screws on the back and gently prize the calculator's rear away from the front, hinging from the bottom. The batteries are fixed to the rear but all the boards are attached to the front.

Logic comments:	(C) cancels an incorrect numerical entry, pressing a second time clears the calculator
	Input overflow is suppressed, keying in a ninth digit is ignored
	Negative numbers are shown with a "-" in the far left (ninth) digit thereby allowing full eight digit negative numbers
	There is no constant on any function
	Overflow shows the result and "o" in the far left (ninth) digit and is not recoverable
	Divide by zero shows "0." and "o" in the far left (ninth) digit and is not recoverable
	Memory system is a confusing: (M) will put a number in memory if used after (=) and (M) will recall the memory is used after an operator.
	There is no indication of memory store - you have to remember it
	It suffers the negative zero bug: key in (1)(-)(2)(=) to give "-1" now (+)(1)(=) will give "-0"
	After 12 seconds my example goes into power save mode showing just "-" in the fifth digit - press any key to continue
	Confusingly (CE) stands for Conversion Entry.
	To convert imperial to metric: (1)(0)(CE)(0) converts 10 inches into centimetres
	To convert metric to imperial: (3)(0)(4)(8)(CE)(M)(1) converts 3,048 metres into feet
	For areas: (1)(0)(0)(CE)(=)(7) coverts 100 sq, miles into sq. kilometres
	For volumes: (1)(0)(0)(0)(CE)(M)(-)(4) converts 1,000 cubic metres into cubic yards

The scan of the inside with the cover removed shows a remarkably low component count for such an early date. The batteries (removed) sit on the blue display ribbon cable connector.

No expense spared in this example as the main cpu has its own socket. Also note the wide range of date codes going from week 10 of 1973 to week 42 of 1974.