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Calculators: Handheld: Boots 425 Scientific

Size (approx): 85mm x 145mm x 22mm (max)  (w,h,d)
Weight 134g excluding batteries

Power:

3.0v DC using 2 x AA size batteries.  Can accept an adapter/charger (3V DC, 0.2W) through a socket on the top side to the far left.  The on/off switch is on the left hand side just above the display. 
Case: Smooth plastic white base and black top.  Above the display is a full-width wrap around metallic sticker, in its own recess, printed black and blue with the brand and model number. A neutral and slightly tilted plastic display filter gives a clean image.  The brushed aluminium keyboard surround is also recessed and printed black, blue and brown with key functions.  Typical Casio keys are squishy but positive with individual plastic escutcheons.
Display: 8 digit blue VFD with a ninth digit for negative indication.  Full nine digits are used in scientific mode as the third digit is used for indicating a negative exponent.
Features: Standard four functions with pi, change sign, reciprocal, factorial, 6 level brackets, square root, squares, DMS input, trigs, logs, powers, reciprocal powers and three-function memory.  Scientific 6+2 display and degree, radian, gradian switching.  Statistical (standard deviation) functions.
Age: 1981
Manufacturer: It just states made in Japan but Casio makes it.  The serial number is inside the battery compartment 1G105A.
Comments:

 

Solid built branded Casio calculator (actually Casio FX-31) that used a familiar layout for years to come.  Displays sexagesimal with a "" symbol.  Sound logic - but limited mantissa, basic memory and lack of error recovery.  The original case is open topped soft black plastic with side cut-outs and made in Japan embossed on the back. 

Components: 1 x cpu: Hitachi HD38111A 1A23 (date code January 1981) 28 pin DIL, 0.6" width black plastic
1 x 9 digit VFD display unit: single tube flat face: NEC FIP9D5 Japan
2 x transistors
11 x diodes
9 x capacitors
3 x resistors
1 x transformer TC-15 TDK
Boards: Main board (Ref G8J-1B) is connected by 21 copper wires to the (and sits on top of the) keyboard board.  The latter is secured to the front by 6 screws.
Construction: Remove the two screws from inside battery compartment, and gently prize from the top pushing sideways to get the switch fully out.  There is a strange (partial) keyboard layout embossed on the front case on the inside.

Logic comments: The Clear key (C) is used to clear an input number, the all-clear (AC) to completely reset the calculator (which does not clear the memory).
Overflow on the input of a number is suppressed, typing in a ninth digit is ignored
The constant function is invoked for all four functions by a double press of the operator:  i.e. (3)(X)(X)(4)(=) 12 (=) 36 etc.
There is no indication of memory use - you have to remember it, and using the (Min) key will overwrite a previously stored number
Negative numbers are shown with a - to the immediate left of a number, travelling into the far left (ninth) digit to allow full eight digit negative numbers
On overflow the display just shows "E" in the far right (first) digit and is not recoverable
On divide by zero the display just shows "E" in the far right (first) digit and is not recoverable
If you try to use more than 6 levels of parenthesis, or functions the display just shows C in the far right (first) digit and is not recoverable
Negative square roots are not allowed and result in an error as above
The change sign function can be used in mid number entry
There is no recovery from any type of error
There is a small exponent display bug: key in the number 12345678 then (EXP) which will display 123456 0.0 showing an erroneous decimal point in the exponent until you press equals
You can enter degrees, minutes, seconds using the ( ' '') key, which it displays in decimal form.  To see it in DMS form use the keys (INV)(<) when upper "" symbols are used to separate the numbers.
Some of the higher functions and all inverse functions are selected using a two key sequence starting with the (INV) key.
Full ten digit precision is preserved try this; "1.01" then square root it until the answer reads "1" then (-)(1) to get 8.9 x 10-8
No major bugs found