Aristo M65

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Calculators: Handheld: Aristo M65

			Size (approx):	62mm x 150mm x 20mm with cover (w x h x d) Weight 122g excluding batteries and cover, 148g with cover
			Power:	4.5v DC using 3 x AA size batteries. It accepts an adapter (centre negative) through a socket on the right hand side just above the keys. Oddly enough, if you use an adapter you must have the calculator switched to the "off" position. You have to take the whole back off to access the three (2 plus 1 separated) battery slots.
			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. Two white switches sit in a recess with more white printed text. A narrow red 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 long travel with a very springy feel. A large black printed metallic 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 individual bubble lens red LED with a ninth digit for negative and error indication
			Features:	Standard four functions with change sign, squares, square root, reciprocal, percentages, register exchange and five function memory. Switched floating and two decimal point mode.
			Age:	1975
			Manufacturer:	Aristo, made by Dennert & Pape AG, Hamburg, Germany. No serial number that I can find but there is the number 303 printed over one of the battery descriptors inside.
			Comments:	This is the first generation range of calculators from the famous slide rule manufacturer. The generic case has a small panel where a third (middle) switch could be. Very clear red LED display and a lovely design that throbs quality. The logic is OK with fair recovery and only let down by the pseudo fixed decimal bug.

Components:	1 x cpu: Unbranded Rockwell A1211 4A (date code January 1974), 42 pin staggered DIL, 0.6" width black plastic with metal lid 1 x IC: ITT XK1696 7509 (date code week 9 of 1975), 16 pin DIL, 0.3" width black plastic 2 x IC: ITT XK1695A 7451 (date code week 51 of 1974), 16 pin DIL, 0.3" width black plastic 3 x 3 digit LED units with individual bubble lens 2 x transistors 3 x diodes 3 x capacitors 5 x resistors 2 x variable resistors 1 x transformer block?
Boards:	The main cpu board (05.01.04.01-1 II) 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 underneath the paper battery instruction label: two at the top corners and two slight inset at the bottom. Warning: very likely to damage the paper label peeling it back - don't do it. The metal plate will then lift away, hinging to the right to avoid breaking the earth cable.

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 and "o" in the far left (ninth) digit and is recoverable using (C)
	Divide by zero shows zero and "o" in the far left (ninth) digit and 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
	The change sign (+/-) can be used in mid number entry but not before
	Negative square roots are not allowed and result in zero and "o" in the far left (ninth) digit and is not recoverable
	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 no indication of memory store you have to remember it
	To add to the memory use (M+) or subtract by (M-) to update the memory use (X <-> M), to recall use (M -> X)
	To clear the memory use (F)(C)
	Memory overflow stores the end result shift by 10⁸
	A [F/2] switch will change the mode between fully floating decimal point and fixed two digit decimal
	It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to give "1.000" which will remain a fixed three digit decimal number until you need more digits or use multiply or divide

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).

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. I think the red block is a transformer unit as it has four connectors.

IC pins bent over for pseudo surface-mounting and an integrated power socket (which uses the back plate as a connector, are used to keep the assembly as slim as possible.