Rockwell 20R

		Home New Stuff Author Links Guest book Web-log	Adverts Bric-a-brac Calculators Components Ephemera Events	For Sale Glossary History Hit or Miss Radios Transport	Ultra Valves Wanted Metal Puzzles Clocks

Calculators: Handheld: Rockwell Memory 20R

		Size (approx):	77mm (max) x 155mm x 22mm (max) (w,h,d) Weight 134g excluding batteries
		Power:	9.0V DC, 1xPP3 size batteries. Also accepts adapter (Part No. 331 R03-001 for the US 110V-120V) through top end socket on the left.
		Case:	Sturdy stippled brown plastic case with light beige keyboard surround. Red display cover shows a clear view of the numbers. Squashy but positive lozenge-shaped keys work well. 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 six function memory
		Age:	1974/5
		Manufacturer:	Rockwell International, Microelectronic Product Division. Made in Great Britain. Serial No. 8A20662
		Comments:	Lovely typical USA Rockwell calculator with sound logic and clear display. 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: A5300PA 7517 (week 17 of 1975) 42 pin DIL 1 x 8 digit (nine bubble lens) LED unit 0 x transistors 0 x diodes 10 x resistors 2 x capacitors 1 x transformer Astec AA1225A
Boards:	Keyboard unit is attached to the main cpu board via eight 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
	Divide by zero shows "0.E" whilst overflows are shown with the answer and "E" in the far right (ninth) digit. The error is recoverable by use of (C). Using "E" means you cannot tell if the overflow is positive or negative until (C) is pressed.
	Minus sign is shown on the far right (ninth) digit
	Input overflow is suppressed, typing in nine digits ignores the last one
	Memory functions are called up by two button presses; i.e. (M) (+) will add the main register contents to the memory
	A non-zero memory storage is flagged by the far right (ninth) digit's decimal point alight
	It has automatic constant on all functions

	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-59-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. My sample has a retailer's stamp on the back; Boots the Chemist Ltd, 49-53 High Street, Dundee.