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Calculators: Handheld: Prinztronic SR99M (type II)

Size (approx):

80mm (max) x 123mm x 21mm (max)  (w,h,d)
Weight 118g excluding batteries
Power: 2.4 to 3V DC, 2 x AA size battery, 0.4W.  Also accepts adaptor/charger (either adapter DC 3V 150mA or charger DC 4V 150mA) through bottom side socket on the right.  The battery compartment cover has a small table showing when an adaptor/charger can be used; Ni-Cd with charger is OK but no batteries must be used with the adapter.
Case: Stylish calculator case in two-piece black (or very dark brown) gloss plastic.  It is dominated by a wrap around brushed aluminium panel on the front.  This is printed with black text for the brand, model name and on/off switch label.  A slightly proud but flat green display filter also wraps over the left hand edge.  They keys are long travel, squishy and very reminiscent of Casio keys.
Display: 8 digit green VFD with a ninth digit used for negative, error and memory indication
Features: Standard four function with percentages, sign change, square root, three function memory
Age: 1975
Manufacturer: Made in Japan, serial No. 607314
Comments: High quality calculator with a stylish design.  The original cover is soft black plastic with an open top and half-moon cut-outs.  There are four documented versions of this calculator.  The logic is poor as there is no recovery, pseudo fixed decimal bug and negative zero bug.

Components: 1 x cpu: Sharp LI2003 5E1 026 (date code January of 1975) 28 pin DIL, 0.6" width 
1 x 9 digit VFD unit: round faced single tube: Toshiba E6532A/DP80B5 5G7G1K
0 x transistor
1 x diodes
5 x capacitors
1 x resistor arrays
12 x resistors
1 x transformer unit: Fuji  UT3111 5F-04
Boards: The main cpu board (68-31A) is placed on top of the keyboard and is fixed by two plastic posts and the adapter socket.  The boards are joined by a 15-way block of wires. 
Construction: Very difficult to open as it is sealed using internal lugs only and the sides of the case are very stiff.  There is what looks like a coin slot at the top - but this appears to be useless.  You have to try and squeeze in the front of the case (on the left), the rear (on the right, top and front) and pop the easiest lug.  Damage is highly like so if in doubt - don't do it.  The back will eventually lift of.

Logic comments: The (C) button is used once to clear entry of a number, a second time to clear the calculator
Overflow on number input is suppressed, keying in a ninth digit is ignored
There is automatic constant on multiplication and division only
Negative numbers are shown with a ?-? sign in the far left (ninth) digit thereby allowing full eight digit negative numbers
The sign change key (+/-) can be used in mid number entry
Overflow shows the result and ?C? (or ?E? if negative) in the far left (ninth) digit and is not recoverable
Divide by zero shows zero result and ?C? in the far left (ninth) digit and is not recoverable
The (M=) keys is actually a memory-plus function, adding the contents of the display to the current memory
To clear the memory use the recall key (RM) twice
Memory store is indicated by a decimal point in the far left (ninth) digit
Negative square roots are not allowed and result in a positive error state which is not recoverable
It suffers from the pseudo fixed decimal bug: key in (1)(+)(0)(.)(0)(0)(0)(=) and the answer is ?1.000? which remains a fixed three decimal number until more digits are required or you use multiply/divide
It suffers the negative zero bug: key in (1)(-)(2)(=) to give ?-1? then (+)(1)(=) will give ?-0?