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Calculators: Handheld: Rockwell 31R (aka Slide Rule Memory) (type I)

Size (approx): 75mm (max) x 155mm x 22mm (max)  (w,h,d)
Weight 176g including battery pack.


9.0V DC, 1xNi-Cd battery pack.  It accepts an adapter/charger (undefined but supplied) through  a socket on the top side to the far left. There is an on/off sliding switch on the left hand side about half way up.  Charging time is quoted as five hours, optimum operating time three hours and "damage your battery time" 72 hours!
Case: Sturdy stippled dark brown plastic case with light beige keyboard surround.  There is an oversized stippled red inset display filter with a smooth window. It has a raised Rockwell logo which along with the front edges is painted silver.  Lovely lozenge-shaped keys in caramel brown have a positive soft click and work well.  The keyboard surround is printed in dark and light brown for the key labels and a designer line.  The model number is printed on the lower edge of the keyboard surround. 
Display: 8 digit LED with bubble lens with a ninth digit (to the far right) for negative and memory indicators.
Features: Four function plus percentages, square root, register exchange, reciprocal, squares, change sign and five function memory.
Age: 1975, this particular example has the guarantee card stamped on 20 Sep 1975 from Boots the Chemist Ltd, Cross Street, Manchester.
Manufacturer: Rockwell International, Microelectronic Product Division, Anaheim CA 92803.  Assembled in Mexico, US and Foreign parts.  Serial number 125300.


Typical Rockwell with a sturdy and unique design.  Trim often wears badly but this example is perfect.  The logic is robust with good recovery and only let down by negative square roots and the pseudo fixed decimal bug. Original case is brown padded plastic with a flip over top flap that tucks in the front.  It is embossed with the word Rockwell.  The rechargeable batteries still work!  Similar to the Mexico built 31R type II.

Components: 1 x cpu: Rockwell A5502P 7523 (week 23 of 1975), 42 pin staggered DIL, 0.6" width
1 x 9 digit bubble lens LED module
2 x capacitors
12 x resistors
1 x transformer: TDK Japan CD-42001 327R05
Boards: Keyboard assembly is attached to the main board (20167D58) by 9 protruding wires that slot into long sockets on the main board.  The transformer is so large that it sits in its own cut-out to reduce the thickness.  Now I know what the push-out hole is for you see on most boards not used.
Construction: Remove the four screws on the back.  Gently pull out the front keyboard which hinges up from the display surround.  Pop off the display surround by pulling it upwards whilst gently pushing a blunt object through the slots at the top of the rear.. Main assembly can be removed by slightly twisting away from the on/off switch.

Logic comments: (C) cancels an incorrect numerical entry, pressing a second time clears the calculator
Input overflow is suppressed, typing in nine digits ignores the ninth
There is automatic constant on all four functions
Negative numbers are shown by a minus in the far right (first) digit thereby allowing full eight digit negative numbers.
The change sign function can be used in mid number entry
Divide by zero results in "" and is recoverable by using (C)
Overflow shows the result with all decimal points alight and is recoverable using (C)
Higher functions are accessed by pressing the (F) key first.  Pressing (F) again will cancel the function mode but there is no indication
Memory store is indicated by a decimal point in the far right (first) digit
(X<>M) exchanges the contents of the memory with the display and register exchange (X<>Y) swaps the two numbers in an operation.
Negative square roots are allowed and result in a negative number
It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to give "1.000" which remains a fixed three digit number until you need more digits or use multiply or divide


warning card manual service sheet
The box is huge at 95mm by 230mm and is 55mm deep.  It is tall enough to accommodate the supplied AC charger.  Printed in buff, light and dark brown it has the words "The Answer" in bold letters down each side.  It comes with a stiff card inner former to keep it rigid.

Stock No. 31R S01, printed in the USA, (c) 1974.

This bold pink extra card appears to be a bit pointless as it has exactly the same text as in the manual.  It warns not to use the calculator for the first 10 minutes of charging and leave the charger connected if you want to use it after 10 minutes.

Ref 2520-D-89 NEW 1-75 (169R05-001)

The manual measures 68mmm by 130mm and is printed in buff (cover only) and black.  Consisting of 52 pages it has extensive examples and instructions in English only.

The rear has the marketing strap line "...where science gets down to business"

(c) Rockwell International 1974, ref. 2520-D-83 (226 R03-016), printed in the USA.

Yet another flier this time reveals that the distributor for this calculator in the UK was Sumlock Anita Ltd.  This is also on the guarantee card (not shown).  As well as returns and repair Sumlock offered a "Calculating Bureaux" which ".. will undertake your regular work (invoicing, payroll, technical analysis etc.), peak workloads (stocktaking, tenders, audits etc.) or temporary operations (to cover holidays and sickness).

They also did machine hire and training!