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Calculators: Handheld: Rockwell the 24K II

Size (approx):

74mm (max) x 137mm x 14mm  (w,h,d)
Weight 92g excluding batteries.

Power: 4.5V DC, 3 x AAA size internal sealed rechargeable batteries.  Also accepts adaptor/charger (undefined, though 3V centre positive got mine working) through a bottom side socket on the left. 
Case: Super slim three-piece metal case calculator with brushed aluminium finish and black plastic mid-piece. Black printed logo, model and keyboard border. Wrap around smooth black plastic display escutcheon with a flat and flush blue display filter is easy to read.  They keys are soft click, medium travel and work well.  Soon all calculators would look like this.
Display: 8 digit blue VFD display with a ninth used for negative and memory indication
Features: Standard four function with percentages, change sign, square root, register exchange and four function memory
Age: 1976
Manufacturer: Manufacturer: Rockwell International, Microelectronic Product Division, Anaheim, CA, USA.  Made in Japan, serial No. not present.
Comments: A solid high quality calculator with a leading edge design that many were to follow into the early days of LCD calculators.  The original case is a black leather wallet with a cradle for the calculator on the left (with a cut-out for the brand logo to show through) and two pockets on the right.  It also has a central pen holder.  The logic is fine with good recovery but let down by negative square roots and the pseudo fixed decimal bug.  Oddly enough it is very similar to the 22K rather than the 24K

Components: 1 x IC: Rockwell A5901CA 7619 (week 19 of 1976), 42 pin staggered DIL, 0.6" width
1 x 9 digit VFD unit: single tube flat face
2 x transistors
4 x diodes
6 x capacitors
7 x resistors
2 x resistor arrays
1 x transformer: Zebra DCT-04B
Boards: The main board (IH-001d) is held in place by three plastic lugs and joined to the keyboard assembly via 12 soldered wires.  You get the message that was was never meant to be taken apart for repair.  The whole assembly is held to the front with four more plastic lugs. The board has a small cut out to allow one of the electrolytic capacitors to sit in and minimise the depth.
Construction: There is a single screw underneath the label on the back - so you will have to damage this top open it.  The back then lifts off easily, hinging from the top.

Logic comments: The Clear key (CE/C) is used once to clear an input number and a second time to completely reset the calculator 
Overflow on the input of a number is suppressed typing in a ninth digit is ignored
The automatic constant is on all four functions
The negative sign is shown in the far left (ninth) digit thereby allowing full eight digit negative numbers.
An overflow is shown with the result and all decimal points alight; it is recoverable using (CE/C).
A divide by zero error results in ? and is recoverable. Using (CE/C).
Negative square roots are allowed and result in a negative number.
The change sign key can be used in mid entry of a number
Memory storage is indicated by the far left (ninth) digit?s decimal point being on.  
The register exchange allows you to swap the last entered number with the one previous (useful for reciprocals)
This calculator suffers from the pseudo fixed decimal bug: key in (1)(+)(0)(.)(0)(0)(0)(=) to give "1.000" which remains a fixed three digit decimal number until more digits are needed or multiply/divide are used

With the back removed you can see the main board and the tray area that held the rechargeable batteries (removed).  Notice the blue electrolytic capacitor in the middle with its own cut-out to reduce the assembly width.