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Calculators: Handheld: Sperry Remington 825-GT 

Size (approx):

116mm x 154mm x 37.5mm (max) (w,h,d)

Weight 282g excluding batteries. 

Power: 6V DC, 4 x AA size batteries.  Accepts an adaptor/charger (AD-4145 0.3W) through a top side socket on the left.  Battery life is quoted as 14 hours for Manganese (dry), and 28 hours for alkaline.
Case: Wide bulky calculator that is made from two pieces of glossy grey plastic case.  There is a black plastic display escutcheon that is slightly tilted up.  It has a neutral filter with two raised white painted lines framing the digits.  Then raised letters sit in their own recess and are painted silver with the company name and model number.  A further black plastic panel sits below in its own recess and has white printed text labels for the switches. They well-ordered keys are quite pronounced, long travel and hollow sounding; they still work very well.
Display: 8 digit blue VFD display with no ninth digit
Features: Four function with square roots, percentages and four-function memory.  Switched accumulating/decrementing memory, switched constant, 16 digit display shift
Age: 1974
Manufacturer: Sperry Remington is a trademark of Sperry Rand Corporation. (Actually made by Casio).  Made in Japan.  Serial number 2102880 on battery compartment cover.  There is another sticker inside the compartment 21004134.
Comments: Big wide calculator that just about fits in the hand but is more likely designed for continuous desktop use.  Unusual early "small zero" (see below) display notation but the display is bright and easy to read.  The original case is soft black plastic with top flaps that close with a top popper. It has Sperry Remington embossed on the front and Made in Japan on the back. The logic is not so good with no recovery, ignorance of zero divisor, negative square roots and loads of bugs, but I do like the two equals keys and lack of semi-RPN input.  This calculator is a branded Casio 801-MR but appears to be a slightly earlier model than the linked one.

Components: 1 x cpu: Hitachi HD3654 4G 11 (July 1974) 40 pin DIL  0.6" width black plastic
1 x 8 digit VFD unit single glass tube round faced
2 x transistors
4 x diodes
16 x capacitors
11 x resistors
2 x resistor arrays
1 x transformer module; Fuji UT 0637 4F-28b (Pat No. 427559) (date code June 1974)
Boards: The keyboard assembly (A8A-E4A) sits lose on top of the main board (A8A-1A) and is connected via 15 strong wires.  The whole assembly sits lose in the calculator.  The inside even has some internal guides on the right hand side to keep the trailing power wires tidy.
Construction: Remove the small screw on the top edge.  Then, starting at the top edge, gently lever out the white front section to pop the two lugs.  Carry on down the sides and eventually you can hinge off the front section from the bottom edge.

Logic comments: The Clear key (C) is used to clear an input number and the (AC) key to completely reset the calculator
Overflow on the input of a number is suppressed, keying in a ninth digit is ignored
Overflow shows the result (in 16 digits) and is not recoverable
Divide by zero does not result in an error - you just carry on with zero result
The selectable constant (K) function operates on multiply and divide only
Negative numbers are shown with a "-" in the immediate left hand digit limiting you to seven digit negative numbers in calculations and 15 digit ones on overflow
The memory is an automatic accumulation type.  Use the (S) key to enable, then every result of the black (=) key is added to memory, every result of the red (=) key is subtracted.  Memory recall (and use in a calculation) is be pressing the (T) total key. Example when switched on: (1+2)X(3+4) is done by (1)(+)(2)(=)(3)(+)(4)(X)(T)(=).  (AC) clears the memory.
There is no indication of memory store other than the blue dot on the (S) switch
Negative square roots are allowed and result in a positive number
The display shift key (>) is used to see the least significant eight digits of an answer whilst held down.
Only the result of certain calculations use the 16 digit capability:
Capacity: Entry/display 8 digits
Addition / Subtraction 15 digits (max 9 digit integer)
Multiplier / multiplicand 8 digits
Divisor / dividend 8 digits
Product 16 digits
Quotient 8 digits (significant figures)
Square root 7 digits
Accumulation into memory 8 digits
It suffers the divide to negative zero bug: with (K) switched on key in (-)(1)(=)(/)(1)(0)(=)(=)(=) etc. to eventually get "-0"
It suffers the negative zero bug: key in (1)(-)(2)(=) to give "-1" then (+)(1)(=) to give "-0"


The manual measures approximately 150mm by 107mm and is 12 black and white pages in total.  In English only it has plenty of examples and instructions.  Printed in Japan.

"Congratulations on your purchase of this personal electronic memory calculator, which you will find perfect for your requirements."

"To utilize the full features of your calculator, no special training is required..."

Note the unusual way that zero is represented - by only using the lower half of the digit.  The main theory about this is that it allowed any particular segment to stop working and you could still identify the number.
Buy this manual pdf.