Sperry 1259S

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Calculators: Desktop: Sperry 1259S (aka EDC1259S)

	Size (approx):	240mm x 315mm x 77.5mm (w,h,d as pictured) Weight 2.3kg excluding cable
	Power:	Mains (110, 117, 220, 230 or 240V 50/60 cycles), 0.19A, 18 watts through a removable cable
	Display:	12 digit nixie with separate neon light for minus indication (see more below)
	Features:	Standard four functions with change sign, sin, cos, tan, arc tan, transcendentals, hyperbolic cos and sin, nth power, square root, cube root, sexagesimal conversion, constant memory, register exchange, degree/radians and four-function memory. Fixed decimal point selection, floating, round and round down.
	Age:	1973
	Manufacturer:	Remington Rand Office Machines Division, serial number 307842, made in Japan.
	Comments:	Fabulous early scientific desk top monster that was a branded Casio FX-1 with a long sleek design. A German edition known as the Deitzgen model ESR-1 is also apparently a clone with a Casio FX-2 a close VFD-based relative. Loads of functions which are made up from discrete logic and ROM so that you can see the intermediate steps in the calculation on the display. Cube root takes up to 25 seconds - glorious to watch. Original cover is white shaped plastic with black plastic piping. As one would expect of such an early calculator, the accuracy of some of the higher functions is a bit low, recovery is absent, and the rest of the logic can be a bit shaky.

Case and Design:

The case is made from two sections of light cream matt plastic with a black painted section for the keyboard surround. A orange plastic display filter is heavily tilted and inset to shade the display. Underneath it are numeral ID numbers. At the bottom of the display is a sliding "thousands" indicator with three white tick marks.

To open remove the four screws that can be access form the underneath. Turn the calculator back over and remove the top section - hinging it to the right.

Three boards (for PSU, Display and CPU) are tiered at three different levels and held by sturdy plastic and metal brackets. The keyboard assembly is fixed to the top section of the case.

Display:

The main numerical display consists of 12 orange coloured nixie display tubes. Each tube has a dot for the decimal point. There is one extra neon lamp to the left of these for the minus sign. As the tubes do not have commas for thousand indication, an external sliding rail is provided.

The display is not suppressed when a calculation is ongoing - you can see loads of intermediate results during the process. There is also no leading zero suppression - all digits are always on.

The display board (LG0102) is the middle tier board and in the image on the left you can see the white plastic tube surrounding the minus indicator to diffuse the neon.

Keys and Switches:

Big chunky keys typical of its era that are long travel and quite noisy. The majority of keys are grouped logically into "higher function" (at the top obviously), memory and clear, numerical and operational functions. The change sign just does not fit in so has its own spot at the top left.

An inset switch panel contains two sliders. The first allows selection between floating, rounding, and round down mode. The second upper slide switch chooses between 0/2/3/4/6/8 fixed decimal digit mode.

The higher functions keys have nice little metallic stickers printed black for their operation. They actually invoke subroutines that are held in ROM chips which explains why the main cpu board is so large.

Too many components to count in this beast. The quality of manufacturing and engineering is superb and was no doubt reflected in its enormous original price. That it still works perfectly today is a testament to the engineering and electronics. The majority of main ICs are NEC ( D174B, D503, µPD101C, µPD312C, µPD358C) but there are also many Hitachi (HD3106P, HD3104P, HD3113P) with date codes of January/February 1973, and quite a few Toshiba (TM4351P) as well.

The main power supply board (IS-54T) sits above the display board and main cpu board, making a third tier. Hefty transformer (upper right) with big heat-sink blocks on transistors (upper left) and big fat capacitors - built to power a major price of apparatus.	One main board (TBL-A LG0166 No. 9454) sit nearly the whole length of the case. This closer view shows the edge of the main board crammed with components - it is this density all the way back. There are a mixture of NEC, Hitachi and Toshiba ICs even in this partial image.	The keyboard assembly (A12E-E4B Kydei) is attached to the front of the case and consists of sturdy metal brackets with moving magnets and glass magnetic reed switches. After over 30 years they have proved to be very reliable.

Logic comments:	(C) is used to cancel the last number or constant function entered and (AC) to clear the whole calculator.
	Input overflow is not suppressed, inputting a thirteenth digit causes all digits to be set to zero and you can carry on keying in the number again
	Logic is semi-RPN, to do 3-4 key in (3)(+=)(4)(-=) to give "-1"
	The change sign function (CHG Sign) can be used in mid number entry
	There is semi-automatic constant on multiply and divide by double hitting the multiply or divide key - just like later Casio pocket calcultors
	Constant memory is switched in with the (Kin) [to add your number into the constant memory] and (Kout) which recalls the memory. This register can only be cleared by entering zero using (AC)(Kin)
	(EXC) is used for register exchange, and is useful for reciprocals
	Overflow shows no result and just lights all the digits as zero and is not recoverable
	Divide by zero shows no result and just lights all the digits as zero and is not recoverable
	Negative numbers are shown with an individual neon left to the right of the main display thereby allowing full twelve digit negative numbers
	Negative square roots are allowed and result in a negative number
	The decimal point switch can be selected between 0/2/3/4/6/8 fixed decimal places - which are ignored if a higher function is used
	There is no indication of memory store - you have to remember it
	To convert from sexagesimal 12° 45' 9" just key in (1)(2)(a°'")(4)(5)(a°'")(9)(a°'") to give 12.7525 degrees
	The power function only goes up the the 9^th power, to find 3⁵ key in (3)(aⁿ)(5) to give "243"
	Calculating times vary from 12 seconds [cube root], through 2.3 seconds [arc tan] to 0.08 seconds for addition
	Not all functions use all 12 digits: trigonometric and log functions use 10 digits whilst square root and cube root use 11 digits
	This calculator suffers a infinite tan bug, (9)(0)(tan) should be an overflow as the answer is infinite, but mine shows what the manual describes as meaningless digits: "063661977316"

Manual:

The large manual is A4 sized black and white only. It has 28 pages and is in English, French and German. Loads of examples cover the use of each key one by one as well as complex calculations and engineering and mathematical examples. Each function is well described with input limitations and accuracies.

Interesting the introduction is missing the English section!

I could only find a few minor translation errors (e.g. page 13 "... is displayed by the dicimal scale."

My example also came with an A4 sheet called a "Field Quality Report" with the model and serial number stamped on it. This green and blue sheet was filled in by the owner on receipt to report and Visible Damage, packing case condition, Hidden Damage, Adjustments and Performance Deficiencies.

Sperry Rand, Remington Rand Office Machines, Printed in Japan.