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Calculators: Handheld: Rockwell Slide Rule Memory 30R

(c) Emil Dudek 2010

Size (approx): 77mm (max) x 155mm x 22mm (max)  (w,h,d)
Weight 134g excluding batteries


9.0V DC, 1xPP3 size batteries.    Also accepts an adaptor (Part No. 331 R03-001 for the US 110V-120V) through top end socket on the left. (This is centre positive).
Case: Sturdy stippled brown plastic case with light cream keyboard surround.  The over-sized red plastic display filter fits flush with the case and shows a clear view of the numbers.  Squashy but positive lozenge-shaped keys work well.  Key labels are printed in dark and light brown.  The raised Rockwell logo and two vertical edges are painted silver and have survived very well on this example.  The on/off sliding switch is on the right hand side midway up.
Display: 8 digit red LED with bubble lens and ninth digit for minus sign 
Features: Four function with percentages and four function memory.  Register exchange, change sign, inverse, squares and square roots.
Age: 1974
Manufacturer: Rockwell International, Microelectronic Product Division.   Made in Great Britain. Serial No. 9A14514


Lovely typical USA Rockwell calculator with some weak logic and bugs.   Both the silver trim and any lettering on the keyboard surround have a tendency to rub off so finding good examples is not easy.   Original case is padded brown plastic with flip top cover and tuck-in tab at the front.

Components: 1 x cpu: Rockwell A4612PA 7506 (week 6 of 1975) 42 pin staggered DIL 0.6" width metal capped
2 x logic gates Texas SN7429A M7432 (week 32 of 1974) 14 pin DIL 0.3" width black plastic
1 x 9 digit bubble lens LED unit 
0 x transistors
5 x diodes
10 x resistors
2 x capacitors
1 x transformer Astec AA1225A
Boards: Keyboard unit is attached to the main cpu board via nine pins into sockets on the bottom and side of the main board.  Later models solders these connections as it reduced manufacturing costs.
Construction: Remove the four screws on the back.  Gently push out the front keyboard which hinges up from the display surround.  Pop off the display surround by using gently pushing a blunt object through the three slots on the rear.  The area above the display has a piece of matt grey card so that light does not show through the upper part of the red plastic cover.

Logic comments: (C) cancels an incorrect numerical entry, pressing a second time (C) clears the calculator
Input overflow is suppressed, keying a ninth digit is ignored
Negative numbers are shown with a minus sign in the far right (ninth) digit thereby allowing full eight digit negative numbers
Overflow shows the shifted result and "o" in the far right (ninth) digit and is recoverable using (C)
Divide by zero shows "0.o" and is recoverable using (C)
There are  automatic constants on all functions
Extra functions (including the memory) are accessed by a two key system using the (F) key, which is not indicated
Memory storage is not flagged - you have to remember it
Overflow in memory is not flagged - and stores the shifted result
Negative square roots are not allowed and result in "0.o" and are not recoverable
The (X<->Y) key can be used to exchange registers
It suffers the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(=) to get "1.000" which remains a fixed three digit decimal until you need more digits or use multiply or divide


The sample manual of the 30R is too poor to scan but is practically identical to the 20R manual pictured on the right.

Small manual measuring 128mm x 68mm has colour cover (including inside diagram) and 48 additional one colour black printed pages.  Back states "Rockwell International ... where science gets down to business".  Ref 2520-D-60-R2-407, Litho in the USA.  Stated copyright of 1974.

Excellent in depth manual with advert in the middle for the whole range that year; 10R, 20R, 30R, 51R, 61R and 80R.