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Calculators: Handheld: Prinztronic Converter

Size (approx): 75mm x 143mm x 23mm (max)  (w,h,d)
Weight 152g excluding batteries.
Power: 6V DC, 4 x AA size battery.  Also accepts adaptor (6V) through a socket on right hand side two thirds up.  Adapter socket is centre positive.
Case: Solid but slightly squeaky two-piece smooth plastic case.  Dark brown base and (originally) white upper half.  Metal keyboard surround has been painted black with silver text and logos.   Green display filter is tilted at about 25 degrees and is lightly shielded by raised sides.  Buttons are short-travel with a positive click and work well on this sample.  Very futuristic with plenty of curves.
Display: 8 digit green VFD with a ninth digit for negative and error indicators
Features: Basic four function with percentages, change sign, square root and many financial functions.
Age: 1975
Manufacturer: Labels missing on my example but suspect made in Taiwan.  Inside battery compartment sticker states serial number 587404 
Comments: Very nice converter calculator that looks to have been made by Qualitron.   Lots of useful conversion functions on top of a basic calculator.  The logic is quite sound with good recovery and only the pseudo fixed decimal bug.   Original case is soft black plastic with zip up side and top.

Components: 1 x IC: Rockwell A4084PC 7502 (week 2 of 1975), 42 pin staggered DIL, 0.6" width
1 x 9 digit VFD module single glass tube flat faced; ISE FG95A HK30D
8 x diodes
3 x capacitors
3 x resistors
2 x resistor arrays
1 x transformer; DCV-4055
Boards: The main cpu board (DI-1439B-A ISE) is attached to the front by two more screws.
Construction: Remove the two screws from inside the battery compartment, under rubber bungs.  There is a third screw underneath the rear label which is impossible to remove without damage.  My example was missing its label anyway so I could look inside.  The back lifts off easily as there are only lugs on the top and left (from the rear) sides.

Logic comments: (C) clears the last number entered whilst a second consecutive press clears the calculator
Input overflow is suppressed, inputting a ninth digit is ignored
There is automatic constant on all four functions
Negative numbers are represented by a minus sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
Divide by zero shows "0.0.0.0.0.0.0.0." and an upper "n" in the far left (ninth) digit and is recoverable using (C), when the display reverts to "0.0000000"
Overflow shows the result with all decimal points and an upper "n" (upper "o" if negative) in the far left (ninth) digit and is recoverable using (C)
It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to give "1.000" which remains a fixed three digit decimal number until more digits are needed or you use multiply/divide
Without a manual, some keys are a bit of a mystery but:
To convert 1 inch into mm key in (1)(CONV)(inch)(mm) to give "2.54"
The A and B keys look like you can store your own conversion factors
There is a switch to select Land/Nautical distances
A further switch selects between US and imperial measurement