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Calculators: Handheld: Rockwell 24RD

(c) Emil Dudek 2010

Size (approx): 75mm x 155mm x 23mm  (w,h,d)
Weight 156g excluding batteries

Power:

6V DC, 4 x AA size  batteries.  Does accept an adaptor (undefined but 4mm plug centre positive worked fine) through socket on the top at the far left. 
Case: Sturdy stippled brown plastic case with light cream keyboard surround with brown printed text.  A neutral plastic display filter site slightly inset to the case edges and gives a clear view of the numbers.  Squashy but positive keys work well.  The raised Rockwell logo and two vertical edges are painted silver and have not worn well in this example.  
Display: 8 digit blue VFD display with no ninth digit but two extra red LEDs above the display to indicate memory storage and minus sign.
Features: Standard four functions, square root, change sign, percentages and four function memory.
Age: 1975
Manufacturer: Rockwell international, Microelectronic Product Division, Anaheim, California 92803.  Made in Japan.  Serial No. 104155.25.
Comments:

 

Classic Rockwell shape made that bit more desirable by the two isolated red LEDs.  Original case is very high quality brown leather-effect with flip over top and tuck in band.  Built to last - but pseudo fixed decimal bug and negative roots let the logic down.

Components: 1 x cpu: Rockwell A5901CA 7551 (date code week 51 of 1975) 42 pin staggered DIL
1 x 8 digit VFD flat panel faced display; ISE DP89A 5927  made in Japan
2 x transistors
7 x diodes
9 x capacitors
2 x resistor arrays
9 x resistors
1 x transformer; DCT24
Boards: The keyboard assembly is attached to the front of the calculator via 12 screws and to the cpu board via 12 strong copper wires. 
Construction: Remove the two small screws in the battery compartment.  Gently pull apart the sides and pull the front out (hinged at the middle.  Pop off the display cover in a similar way.

Logic comments: (CE/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 indicated by a pin-point red LED thereby allowing full eight digit negative numbers
Overflow displays the shifted number with all decimal points lit and is recoverable by using (CE/C)
Divide by zero shows "0.0.0.0.0.0.0.0." and and is recoverable by using (CE/C)
It has automatic constant on all functions
The change sign function can be used before, during and after a number entry
Memory storage is indicated by a second isolated red LED above the display
Overflow in memory is flagged and maintains the original number
Negative square roots are allowed
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