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Calculators: Handheld: Elka 101 (type II) (yellow)

Size (approx): 70mm x 135mm x 30mm (max)  (w,h,d)
Weight 126g excluding batteries

Power:

6.0V DC, 4 x AA size batteries.    Also accepts adapter (undefined) through top side socket on the right. 
Case: Lovely solid yellow backed calculator with smooth rear and slightly matt black front piece.   Brushed aluminium panel with black printed text surrounds switches.  Back top of calculator is raised by about 30 degrees and the orange display filter raised even more with a "fine-line" design.  The lower front edge has the brand and model number printed in white.  A typical 70s design that was also available in green (and maybe more colours).    Flat red LED display appears to have segments made up of small dots (about four) and does not suffer from the narrow angle of view of the usual bubble lens LEDs. The keys are squishy, medium travel and work well enough.
Display: 8 digit red LED with bubble lens and ninth digit for minus sign, error and memory flag
Features: Four function with percentages and two function memory.  Switches for F/2/4 point definition and memory on/off.
Age: This one is 1975 but the design goes back as far as 1973.
Manufacturer: Produced by ISOT, exporter: ISOTIMPEX. Made in Bulgaria.  Serial number 251775 on sticker in the battery compartment.
Comments:

 

Lovely solid calculator, especially for its age.  Original leatherette case is 70% zip-around.  My example comes in a further outer hard plastic case which I cannot validate if it is original or not - can you help?  You can see a different model (with the same name) in green without the decimal point switch and different display. 

Components: 1 x cpu: Rockwell A4130PA 7521 (week 21 of 1975) 42 pin DIL, 0.6" width
1 x logic chip BD5025 7403 16 pin DIL, 0.3" width
1 x nine digit flat LED display
20 x transistors
2 x diodes
17 x resistors
5 x capacitors
1 x transformer TP022
Boards: Small cpu board is connected to the full sized keyboard and display board by 30-way ribbon cable. Board are secured using the case fixing screws.
Construction: Remove the four screws on the back.  Two of these screws are hidden underneath the sticky "model number" label.  The case easily separates.

Logic comments: (C) cancels an incorrect numerical entry, pressing a second time (C) clears the calculator
Divide by zero shows "C" in the ninth (far left) digit,  whilst overflows are shown with the answer and "C". The error is recoverable by use of (C).  A negative overflow generates an "E".
Minus sign is shown on the far left (ninth) digit
Input overflow is suppressed, typing in nine digits ignores the last one
Memory is switched on which then stores the accumulative answer from the result register.  
There is a switch for F - floating decimal point, 2 - two decimal places and 4 - four decimal places
Memory storage is flagged by the ninth (far left) decimal point.
It has automatic constant on all functions