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Calculators: Handheld: Casio Pocket-mini (aka P-810)

Size (approx): 60mm x 100mm x 23mm  (w,h,d)
Weight 78g excluding batteries


3V DC, 2 x AA size batteries.  Also accepts adapter (use AD-2S 3V 0.2W) through a socket on the right side at the far bottom.  The on/off switch is on the left side, at the top.
Case: Compact smooth two-piece black plastic calculator with full-cover aluminium inset on the front and half of the sides. Both end sections have a ridged design.  Shaped a bit like a hip flask, the rounded corners make it nice to hold.  The logo and name are silver printed raised letters on a raised display escutcheon.   A neutral and flat display filter gives a clean bright image.  Typical Casio buttons, squishy but work positively.
Display: 8 digit blue VFD with no ninth digit
Features: 4 function calculator with percentages and automatic, one function memory
Age: 1975
Manufacturer: Casio Computer Company Ltd, Made in Japan.  Serial number inside battery compartment 0928107 and  on the cover 6119498. 


Compact palm-sized deign that still feels quite robust.  The logic is weak with no recovery, basic memory, seven digit negative numbers and the negative zero bug.  Still, cute though.

Components: 1 x cpu: Hitachi HD3691 5H 13 (date code of August 1975), 28 pin DIL, 0.6" width
1 x 8 digit VFD; single tube round face 
7 x capacitors
2 x resistors
2 x resistor arrays
1 x transformer module; Fuji HPS 0612 5F-26 Pat No. 427559
Boards: The keyboard assembly (B8N-E4A) is fixed to the front with two screws.  It is attached to the floating main cpu board (B8N-1A) via 13 strong wires.
Construction: Remove the screw from within the battery compartment.  From the back gently pop the two lugs on the left side and then on the right.  Do this by gently pushing in the front section.  There is also a lug to pop in the battery compartment.  The rear section will eventually lift away.

Logic comments: The (C) button is used to clear last entry of a number and (AC) to clear the whole calculator
Overflow on number input is suppressed, keying in a ninth digit is ignored
An overflow error is flagged by a "E." in the far right (first) digit and is not recoverable
Divide by zero results in a  "E." in the far right (first) digit which is also not recoverable.
There is automatic constant on multiply and divide only
Negative numbers are flagged by a "-" sign in the immediate left digit.  As there is no ninth digit you are limited to seven digit negative numbers
The memory is an automatic accumulator: any result of (=) is added to the memory and recalled by (MR)
(C) will clear the memory
This calculator has the "negative zero bug"; key in (0)(-)(1)(=) to give "-1" then (+1)(=) will give "-0"