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Calculators: Handheld: Adler 81C

Size (approx): 75mm x 120mm x 20mm  (w,h,d)
Weight 134g excluding batteries

Power:

6V DC, 4 x AAA size battery.  Also accepts adapter (undefined).  Socket is on bottom side on the right.  Socket is 2mm jack-plug, centre negative.
Case: Square case with back and sides made of one piece of brushed aluminium.  Dark brown plastic calculator body slides down nearly half way to reveal battery compartment.  Pronounced ridges on the side to aid grip.  Squishy but positive action buttons.  Logo and model number is pained on inset panel.  Logo is also painted on the top side.
Display: 8 digit green VFD (ninth digit for error and negative flags)
Features: 4 function calculator with percentages, four function memory with automatic switched summation.
Age: 197?
Manufacturer: TA Vertriebs GmbH, D8500 Nurnberg, Germany.  Type EC 23B, Serial No. 68.793.592
Comments:

 

Unusual slide out design clear display and weighty quality-feeling calculator.  Button colours are a bit of a jumble  but floating decimal and summation switches are a bonus for this early calculator.  Black plastic case is open topped, rigid front and back and very square in design.
 

Components:
Boards:
Construction:

Logic comments: The (Cl) button is used to clear last entry of a number and (C) to clear the whole calculator
Overflow on number input is not suppressed, typing in a nine digit number results in a "C" in the ninth digit, but it is recoverable using (Cl)
An overflow error is flagged by a "C" in the ninth digit, "E" if negative.  It is recoverable using (Cl).
Divide by zero results in a  "C" which is not recoverable.
There is automatic constant on multiply and divide, there is constant on plus and minus by hitting the (+) and (-) key repeatedly. 
Negative numbers are flagged by a "-" sign in the ninth digit.  Memory store is flagged by the ninth decimal point.