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Calculators: Handheld: Rockwell 204 Financier

Rockwell 204

Side view of Rockwell 204 with leg out

Size (approx):

85mm (max) x 160mm x 45mm (max)  (w,h,d)
Weight 208g excluding batteries.
Power: 6.0V DC, 4 x AA size batteries.  Also accepts adapter/charger (undefined) through a top side socket in the middle.  Back panel contains note saying "Use Unicom Ni-Cad battery charger to recharge.  Allow 7 hours for full charge.  Do NOT use battery charger with Ni-Cad batteries removed."
Case: Chunky two piece beige matt plastic case.   Neutral display filter has raised painted logo and model ID.  Also raised but unpainted labels for OVF (overflow) and MINUS lights.  Case is raised towards the back which matches the raised forward keys.  Rear full-width leg pulls out to stand the calculator at an even greater angle.  Battery compartment cannot be moved without raising this leg.  Compartment has ribbon pull for battery removal. Lovely two-tone green key colours.
Display: 8 digit blue/green VFD display.  Additional two discrete red 4mm LEDs for overflow and minus indication.
Features: Switch between BUS (Business) and ALG (algorithmic) functions.  Ten financial functions, ten maths functions - help I need an instructional manual!
Age: 1974
Manufacturer: Unicom Systems, Rockwell International , Sunnyvale, California 94086.  Assembled in Mexico.  Serial No. 510508-50
Comments: Early Rockwell pocket calculators at it's best!  Financial calculators appear to have faded out in the eighties so these rare beasties are well worth seeking out.  This is one of the first true Rockwell calculators.  Although they had made ICs from the very early days it wasn't until Rockwell bought Unicom (in 1972) that they started their own brand.  These "Transition Models" are renamed Unicom calculators. 

Components: 1 x cpu; Rockwell A4061PA 7436 (Week 36 1974?) (20 pin DIL)
1 x logic chip M7426 SC5889P (8 pin DIL)
1 x 8-digit blue VFD display; ISE DP89A No. 732 Japan
2 x red LEDS
6 x transistors
25 x resistors
12 x diodes
5 x capacitors
1 x smoothing choke
Boards: One main cpu board attached by numerous wires to the keyboard board.  There is no board ID.
Construction: Remove single screw from battery compartment and gently lift up the back panel.  Two more screws then hold down the whole board assembly to the front panel. The main board is taped to the case.

Logic comments: The Clear key (C) is used once to clear an input number a second time to completely reset the calculator
Overflow on the input of a number is suppressed
The constant function is automatic on multiply and divide operators only
The calculator defaults to two decimal places.
Negative square roots are allowed.  Square root of six takes two seconds!
A divide by zero lights the left red LED and shows "0.00". Overflow error is shown by the same LED and is recoverable using (C)