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Calculators: Handheld: Prinztronic MC95

(c) Emil Dudek 2010

(C) Emil Dudek 2010

Size (approx): 112.5mm x 175mm x 46.6mm (max)  (w,h,d)
Weight 604g including batteries


Internal rechargeable batteries (7.2V).  It accepts an adaptor model MC95R, 8.7V (1.3W) and 9.6V (1.9W)  through a three-pin socket on the top side just left of the on/off switch.  Battery charging time is quoted  as 3 to 5 hours whilst battery life is quoted at 3 hours.  A 12V car adaptor was also available as an option.
Case: The main case is made from a two-piece dark blue matt plastic and light blue smooth frame with a brushed aluminium panel for the keyboard surround. On the top right of this panel is a translucent sticker explaining the constant indication and cancel function. The on/off switch sits at the top front, in its own recess with white printed label text. Above the display is a black printed metallic sticker in its own recess with the brand and model number.  A green plastic display filter is inset and tilted with the case and is printed with small white digit numbers.  The large keys are long travel with a hollow plastic clunk making it like early desktop.  The left side has a sturdy metal clasp for a carry strap.
Display: 8 digit green VFD  with an extra symbol cluster for display shift, negative, memory, battery low and constant indicators
Features: Standard four function with change sign, three function memory.  Semi RPN (Reverse polish notation) logic.
Age: 1972
Manufacturer: Prinztronic, Dixons International, made in Japan, serial number D2016589


This heavy, well built monster just about fits in the hand but is happier on the desktop,  though Prinztronic tried to push this as a "pocket" calculator.  As well as the archaic semi-RPN input, the logic is poor, with no recovery and plenty of bugs.  However, the memory and 16 digit answers is useful. Stuffed with components as you would expect from this early model - I suspect it was made by Sharp.

Components: Main board:
2 x cpu:
  Rockwell 10580PA 7223 (date code week 23 of 1972), 42 pin staggered DIL, 0.6" width black plastic with metal cap
  Rockwell 10631PA 7222 (date code week 22 of 1972), 42 pin staggered DIL, 0.6" width black plastic with metal cap
4 x IC:
  3 x NEC uPD193C P26156F, 16 pin DIL, 0.3" width black plastic (display drivers)
  1 x Hitachi HD9005 2G (July 1972) 16 pin DIL, 0.3" width black plastic
8 x Futaba VFD tubes (one of which is a display cluster)
3 x transistors
8 x diodes
3 x capacitors
18 x resistors
2 x resistor arrays
1 x NiCd rechargeable battery pack, 7.2V, 450mAh 082B
Power supply board:
3 x transistors
6 x diode
9 x capacitors
8 x resistors
1 x transformer (voltage converter) 
Boards: The main cpu board (4742-A) is mounted face up on top of the keyboard assembly and held in place by two sturdy metal brackets and by screws.   A smaller power supply board (Sanken) is also held face down and held in place by a plastic bracket and four screws. These two board are connected together by a five-way clear plastic connector to allow easy servicing.  The display tubes are held in place by another sturdy metal bracket and connected via a 17-way gold plated connector.
Construction: Remove the two screws from the rear of the case.  This rear section can now be gently pushed upwards to remove it, hinging from the top edge.

Logic comments: The (C) key is used once to the last entry whilst a second press will clear the calculator
Input overflow is not suppressed: keying in a ninth digit results in an overflow "" which is not recoverable
There is automatic constant on multiply and divide only and it is indicated by the "K" display in the right symbol cluster.  For multiplication the constant becomes the multiplicand (first number) whilst in division the constant becomes the divisor (second number).  The constant is reset by using the (-=) key.
Double capacity calculations (up to 16 digits) are possible using multiplication and division but not with addition and subtraction.  In multiplication switch between the upper and lower digits of the product by depressing the (<->) key.  However, when you use a double capacity number to multiply another the lower eight digits are regarded as zero.  Also if you use a double capacity number as a dividend only the upper eight digits are obtained as a result.  The lower eight digits are cleared to zero but the decimal point will be in the right place.
Double capacity display is indicated by "<->" in the far right symbol cluster when viewing the least significant digits
This "<->" indicator is also used as a "battery low indicator
Overflow shows "" and is not recoverable
Divide by zero shows "" and is not recoverable
There is no trailing zero suppression on the results of division or multiplication: (5)(/)(2)(=) gives "2.5000000"
Negative numbers are shown with a minus sign in the right hand symbol cluster thereby allowing up to 16 digit negative numbers
The logic is semi-RPN or arithmetic, i.e. to calculate 3-4 key in (3)(+=)(4)(-=)
Memory store is indicated by a "I" displayed in the far right symbol cluster
Overflow in memory is not flagged and stores the shifted number
The memory is not double capacity so numbers larger than eight digits, but smaller than 17 are held with no lower digits
Change sign can be used in mid number entry but not before: it suffers the negative zero bug if you try; key in (+/-)(1)(C) will give "-0"
It suffers the negative zero bug, key in (1)(+=)(2)(-=) to give "-1" then (1)(+=) to give "-0"
It suffers the pseudo fixed decimal bug, key in (1)(+=)(.)(0)(0)(0)(+=) to give "1.000"  which remains a fixed three decimal digit number until you need more digits or use multiply or divide.
It suffers the divide to negative zero bug: key in (1)(+/-)(/)(1)(0)(=)(=)... etc until you eventually get to "-0.0000000"

Prinztronic MC100 manual

The manual measures 152mm by 122mm and is 40 pages in all.  The cover is half-tone blue and black whilst the inner pages are blue, black and red.  It is in English language only and printed in Japan.  It has loads of specification, examples, instruction and hints.  Did people have bigger pockets in the 1970s?


"The amazing Prinztronic MC100 incorporating two ELSI (Extra Large Scale Integration) marks another major advancement in the world of space age miniaturization.  Years of pioneering research in electronic engineering has led to the development of this most remarkable personal electronic calculator.  The Prinztronic MC95 with its memory register and double capacity mode offers maximum portability with a wide range of mathematical versatility. Calculations are carried out on the MC95 with amazing speed, efficiency and the upmost [sic] reliability."

Prinztronic MC95 box Prinztronic MC95 box

Prinztronic MC95 adaptor MC95SR (C) Emil Dudek

The very large box measures 293mm x 156mm x 154mm (w,d,h) and is top-opening with an inserted plastic carry handle. It has a polystyrene former to position the calculator (and I presume power supply, carry case, strap and manual).  It is printed in half-tone black and blue.  The bottom is printed with the voltage, what looks like a red QA Japanese symbol and the serial number of both the calculator and power supply. The AC adaptor is patterned blue plastic with a red LED to indicate charging.  240V 50/60 Hz, 5.5W.  All-in weight with a UK three-pin plug is 536g.  Serial number 2018469. made in Japan. One side has a (approx.) 2.1m grey mains cable, the other a curly black cable of 18cm (relaxed) - so it was meant to sit on the table with the calculator.

(c) Emil Dudek 2010 This scan on the left shows the calculator with the rear removed and the internal battery pack lifted out of view.  Stuffed full of ICs and components as you would expect from this early age.  Very well built with numerous metal brackets and gold plated connectors, no expense spared and very easy to service.  The board to the left is the power supply/recharge regulator circuit.

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