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Calculators: Handheld: Adler 81CS (aka EC41)

Size (approx):

78mm x 147mm x 15mm  (w,h,d)
Weight 112g excluding batteries

Power: 3.0V DC, 2 x AA size batteries.  Also accepts adapter/charger (undefined) through a socket on the top side on the left. 
Case: Slim tall (squeaky) case made from matt black plastic with a full front wrap around aluminium panel.  The latter is printed with black text for the switch labels.  Large display escutcheon is actually the front of the case showing through. And is printed silver with the make and model number.  Small green display filter gives a very bright image.  The upper escutcheon is so large as this is the section that sits under the PVC pocket in the wallet.  Colourful keys are soft but work well.
Display: 8 digit green VFD (ninth digit for error, memory and negative flags)
Features: 4 function calculator with percentages, delta percentage, change sign, powers, reciprocal, square root, pi and four function memory.  Switch for algebraic / business input principles.  Switch for summation of answers to memory.  Switch for Floating/0/2/3 decimal points.  On/off switch can also be set to “5/4” round down position.
Age: 197?
Manufacturer: TA Vertriebs GmbH, D8500 Nurnberg, Germany.  Type EC 41, Serial No. on battery cover 72735774
Comments: Quality calculator from Adler adopting the leading edge idea of a  “wallet cover”.  However, just to be different the holding pocket is at the top not the bottom, which was more common.  Host of features and a switch to get rid of that annoying Business input mode.  However, switchable reverse polish notation is very unusual. The original case is black stiff plastic with a PVC pocket on the left for the calculator and one on the right, presumably for the manual.

Components:
Boards:
Construction: Cannot find an easy way to open it without the possibility of damage.

Logic comments: The (C) button is used to clear last entry of a number and pressed again to clear the whole calculator

Overflow on number input is suppressed; typing in a nine digit number ignores the last digit 

An overflow error displays the result and "C" in the far left (ninth) digit ("E" if negative) and is recoverable using (C).
Divide by zero results in a  "C" which is not recoverable.
There is automatic constant on all four functions 
Negative numbers are flagged by a "-" sign in the fare left (ninth) digit thereby allowing full eight digit negative numbers.
Memory store is indicated by the far left (ninth) digit decimal point.
A total accumulator for the memory can be switched on with the Σ switch.
The change sign function can be used in mid number entry
Square roots of negative numbers are not allowed; the result is displayed with “E” in the far left (ninth) digit and is recoverable using (C)
The business input mode is Reverse Polish Notation (RPN); the algebraic is as you would expect from a standard calculator.   In RPN mode to work out 3-9 key in (3)(+)(9)(-).  Algebraic input mode is (3)(-)(9)(=) as expected.