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Calculators: Handheld: Prinztronic C-MOS 1 

Size (approx):

80mm x 120mm x 16-26mm  (w,h,d)
Weight 120g excluding batteries
Power: 1.5V, 1 x AA size battery.  It accepts an adaptor (undefined, 1.5V centre positive) through a socket on the top side to the far left. 
Case: Wedge shaped calculator made from two-piece smooth and matt black plastic.  The front section is spray-painted silver which on my example has worn at the edges a bit.  The upper section is dominated by an oversized neutral display filter that is printed white and blue for the brand and model number. This filter is slightly raised but is flat to the calculator body and gives a clean, deep image of the digits.  The keys are quite proud with a squishy and wobbly action but work quite well.   The keyboard surround is a matt black plastic panel.
Display: 8 digit blue VFD with a ninth digit for negative and error indication
Features: Standard four function calculator with percentages, and square root.
Age: 1976
Manufacturer: No information on the other than made in Japan, no serial number.
Comments: Nice clean design although basic in its capabilities.  There were a number of models in this range ? this being the most basic.  I think the name comes from the IC fabrication type: Complimentary Metal Oxide Semiconductor to make is sound modern and high-tech.  The logic is, quite frankly, a mess.  Trailing zero bug, pseudo fixed decimal bug, root-zero bug all appear to be linked in this model.  Coupled with no recovery I beginning to think that CMOS stands for Complete Mass Of S?  It appears to be a Toshiba calculator inside and is almost identical to the Toshiba BC8013.

Components: 1 x cpu: Toshiba T3332 6D (April 1976), 28 pin DIL, 0.6" width
1 x 9 digit VFD unit: round faced single tube: Toshiba E6536 6F (June 1976)
1 x transistor
6 x diodes
5 x capacitors
6 x resistors
1 x transformer unit: TDK A-092
Boards: The keyboard assembly (67F06687) sits on top of the main board (Toshiba 4468660000 4468650000) and is connected by a plastic covered block of 17 wires.  The whole assembly sits loose in some guide rails.
Construction: Inside the battery compartment you will see a small plastic lug; lift this and the top section will ping open.  The front will then easily lift off.

Logic comments: (CE) cancels the last number entered whilst (C) clears the whole calculator
Overflow on number input is suppressed, keying in a ninth digit is ignored
Negative numbers are shown with a ?-? sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
There is automatic constant on all four functions
Overflow shows the result and ?E? (negative or positive) in the far left (ninth) digit and is not recoverable
Divide by zero shows ?0.? and ?E? in the far left (ninth) digit and is not recoverable
The (%) key just divides by 100 and can be used repeatedly (this also generates the trailing zero bug.
Negative square roots are not allowed and result in a zero overflow and is not recoverable
It has the square root of zero bug: key in ?0?(√) to give ?0.0000000?
It has the trailing zero bug: key in (1)(0)(0)(/)(=)(=)(=) etc. until you get ?0.0000000?.  Trailing zeros will now stay when you perform subsequent operations
It has the negative zero bug: key in (1)(-)(2)(=) to give ?-1.? now (+)(1)(=) will show ?-0.?
It has the pseudo fixed decimal bug: key in (1)(+)(0)(.)(0)(0)(0)(=) to give ?1.000? which will remain a fixed three digit decimal number until more digits are required.

With the front removed and the keyboard assembly pulled back you can clearly see the main board.  A surprising number of links could surely been avoided with a slightly better design.

You can just see the block of cables at the bottom that attach to the keyboard.