Aristo M66S

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Calculators: Handheld: Aristo M66S

			Size (actual):	78.0mm (max) x 151mm x 20.5mm with cover (w x h x d) Weight 150g excluding batteries and cover, 184g with cover
			Power:	3.0V DC using 2 x AA size batteries. It accepts an adaptor (undefined) through a socket on the top side to the far left. You have to take the whole back off to access the three (2 plus 1 separated) battery slots, one of which is not used.
			Case:	The base is a well shaped gloss and matt white plastic piece whilst the front section is matt black plastic. The top area has white printed text with the brand and model number. A white on/off switch sit in a recess with more white printed text. A narrow smoke-coloured plastic display filter sits flat and flush and gives a bright, easy to read display. The slightly recessed keyboard area has white printed text for the higher functions. A lower area has the country of origin in even more white printed text. The keys are medium travel with a very springy feel and soft click. A large black printed grey panel on the back has instructions in German and English and sits in its own recess. A full-frontal smoked plastic cover does a good job of protecting the calculator.
			Display:	8 digit blue VFD with a ninth digit for negative and memory indication
			Features:	Standard four functions with change sign, squares, square root, reciprocal, percentages, pi, register exchange and five function memory.
			Age:	1977
			Manufacturer:	Aristo, made by Dennert & Pape AG, Hamburg, Germany. Faint embossed serial number on the rear sticker: 2LL04 0296.
			Comments:	This is a later generation of the range of calculators from the famous slide rule manufacturer. The generic case has small panels where another two switches could be. Reasonably clear display and a lovely design that throbs quality. The logic is only half tested. Rather confusing that the rear label refers to it as the M66 - which was another model - so probably a revision.

Components:	1 x cpu: Rockwell A5553CA 7727 (date code week 27 of 1977), 42 pin staggered DIL, 0.6" width black ceramic with black lid 1 x 9 digit VFD units glass tube flat faced 3 x transistors 2 x diodes 4 x capacitors 4 x resistors 2 x Resistor arrays 2 x variable resistors 1 x choke
Boards:	The main cpu board (Aristo M66 05.16.02.01-1 IIa) is fixed to the front with plastic lugs whilst the keyboard assembly sits underneath.
Construction:	Remove the dust cover from the front. Prize up the front section of the calculator by putting a blunt implement in the lower edge slot (as you would do to change the batteries). A metal plate then shrouds the main assembly. There are four screws. The metal plate will then lift away.

Logic comments:	The (C ) key is used to clear the last entry whilst a second press clears the whole calculator so it is really a (CE/C) key
	Input overflow is suppressed, keying in a ninth digit is ignored
	There is automatic constant on all four functions
	Negative numbers are shown with a "-" sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
	Overflow shows the result with all decimal points on is recoverable using (C)
	The register exchange key (x<>y) will swap the contents of the display for the last number entered whilst the memory exchange (X <-> M) will swap the current display with the memory
	Higher functions are accessed by a two-key sequence using the (F) key first; the square of 2 being calculated by (2)(F)(X²) to give "4"
	There is indication of memory the decimal point of the far left (ninth) is switched on
	Memory functions are a two-key sequence: i.e. to add to the memory use (M)(M+)
	Brief description as my model failed to work after a few minutes

	The image left shows the calculator with the rear section and metal screening plate removed. Notice the battery compartments, two on the top and one on the bottom (right); the latter is not connected. What looks like un unbranded Rockwell IC is accompanied by three ITT ICs with high quality tantalum bead capacitors and no expense spared variable resistors. Compare with the earlier Aristo M65 inside (opens new window).
	IC pins bent over for pseudo surface-mounting are used to keep the assembly as slim as possible. Notice also that a lot of the pins of the IC are never connected - it can do much more!