Adler 121C EC29

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Calculators: Handheld: Adler 121C (aka EC29)


		Size (approx):	85mm x 148mm x 25mm (w,h,d) Weight 208g excluding batteries
		Power:	6V DC, 4 x AA size battery. Also accepts adapter/charger (type AD40, 41, 42, 43 or 44) through a socket on the top side to the far left.
		Case:	The main body is made from two pieces of very dark brown matt and smooth plastic. This is surrounded by a “U”-shaped aluminium rear that wraps around the sides. Ridges are featured on the sides to aid grip. This piece can slide up and down to get access to the battery compartment and eventually, to dismantle the whole calculator. A recessed and tilted green plastic display filter has faint white printed text underneath it. Below the display is a black printed metallic sticker that sits in it own recess. The keys are quite squishy with medium length travel and a soft click. The matt keyboard surround is printed with white text for the switch labels.
		Display:	12 digit green VFD with a thirteenth digit for negative, overflow and memory indication. Numbers are left starting rather than the normal right used today.
		Features:	4 function calculator with percentages, square root, register exchange, constant store and four function memory. Switched summation / accumulation modes. Switched percentage function. Switched decimal modes.
		Age:	1975
		Manufacturer:	T-A Vertriebs GmbH, D8500 Nurnberg, Germany. Type EC 29, Serial No. 65511502N
		Comments:	Unusual slide out design clear display and weighty quality-feeling calculator. Button colours are a bit of a jumble. Fabulous stack of functions (more associated with a desktop) with an unusual assignable percentage function, 10+2 digit mode and extra constant memory. Only let down by negative square roots, no recovery input overflow and divide by zero bug.

Components:	1 x cpu; Omron HD3687 5E51 (date code May 1975) 36 pin DIL, 0.6" width black plastic 1 x IC: underneath the display so cannot identify it, 40 pin DIL, 0.6" width black plastic 1 x 13 digit VFD; single tube flat face 2 x transistor 8 x diodes 11 x capacitors 7 x resistors 3 x resistor arrays 1 x transformer
Boards:	The keyboard assembly sits on top of the battery compartment and is attached to the main cpu board (T121C-340402A) below with a 19-way ribbon cable. This whole assembly sits lose in the case.
Construction:	Remove the u shaped metal back piece by gently sliding it all the way off. Then remove the two screws from within the battery compartment. The front of the case will then lift off easily.

Logic comments:

The (C) key is used one to cancel the last number entered whilst a second press will clear the calculator

The logic is RPN (Reverse Polish Notation): to do 4-7 key in (4)(+=)(7)(-=) to give “3”

Display is left leading rather than the now common right reading

Overflow on number input is not suppressed, typing in a thirteenth digit causes an overflow state, showing the input number and "C" in the far left (thirteenth) digit, which is not recoverable

An overflow error shows the result and “C" (“E” if negative) in the far left (thirteenth) digit and is recoverable using (C)

Divide by zero just results in zero answer with no error – you can carry on calculating

Negative square roots are allowed and result in a positive number

Constant use is manual by storing the number using the (K in) key and using it with the (RK) recall key

Negative numbers are flagged by a "-" sign in the fare left (thirteenth) digit thereby allowing full twelve digit negative numbers

The percentage key just divides by 100 in standard mode

Rather unusually you can change the function of the percentage key with a switch labelled:

	%+/- makes it operate like a normal percentage key
	TAX uses the value of the K register divided by 100: (5)(Kin)(50)(X)(%) gives you 5% of 50, “.25”
	Delta % returns the difference between two numbers
	MU marks up the number by a percentage
	PR returns the percentage ratio

The (EX) key exchanges the last two numbers entered – useful for reciprocals

There is a decimal point mode switch to change between financial input (AM), floating (F) and fixed digit (0/1/2) – a setting, which is ignored for square roots

The (n) switch puts the calculator in count mode; two of the right most digits total the number of calculations you do which is useful for checking the quantity of numbers you have added together. You can only use the calculator as a ten digit machine in this mode.

The (A) switch adds the result of any multiply/divide calculation to the memory automatically.

You can add to the memory (M+), subtract (M-) recall (Mout) or clear (MC)

Memory store is indicated by the decimal point of the far left (thirteenth) digit