Litton Royal RC-84

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Calculators: Handheld: Litton Royal RC-84

		Size (approx):	87mm x 158mm x 15-37mm (w,h,d) Weight 168g excluding batteries
		Power:	6.0V, 4 x AA size batteries. It accepts an adapter (6V DC 0.5W) through a socket on the top side to the far left.
		Case:	It is a heavily wedged shaped two-piece dark brown and beige matt plastic case. The neutral plastic display filter has a window for the digits to show through and is curved to fit flush against the top of the case. A large front brushed aluminium panel is surrounds the keyboard and is printed dark grey with the brand name. It is further surrounded by a brown plastic escutcheon. The keys are wobbly and soft with a faint click. The on/off switch is on the left hand side, level with the display. The rear has a full-width felt foot at the bottom to stop slipping on a table.
		Display:	8 digit blue VFD, with a ninth digit for minus and error indication.
		Features:	4 function calculator with percentages and square roots
		Age:	1976
		Manufacturer:	Litton Royal-Imperial International, Frankfurt, W. Germany. Serial number 1252965.
		Comments:	Solid built and ideal for the desk-top but can be hand held equally as well. The original case is soft black plastic with a top flap and front Velcro closing. The logic is sound except for the zero square root bug and its cool to watch square roots cycle all the digits for a second.

Components:	1 x cpu: Texas TMS 0855NL KAS 7620, 28 pin DIL, 0.6" width 1 x 9 digit VFD single tube round face, single connection end: Itron DP95A 1 x transistor 3 x diodes 5 x capacitors 2 x resistor arrays 4 x resistors 1 x transformer: F-12
Boards:	The main cpu board (560501A2) is fixed to the back section by some plastic pillars. It connects to the front-mounted keyboard assembly (KB-1096658) via 19 strong wires.
Construction:	Remove the single screw from inside the battery compartment. You can then pop the internal lugs by gently squeezing in the front section. The two halves will separate, hinging off the bottom.

Logic comments:	The (CE) button is used to clear last entry of a number and the (C) clear the whole calculator.
	Overflow on number input is suppressed inputting a ninth digit is ignored
	An overflow shows the result with a “u” (or “o” if negative) in the far left (ninth) digit and is recoverable using CE
	Divide by zero results in zero and a "u” in the far left (ninth) digit and is recoverable using (CE)
	There is automatic constant on all four functions
	Negative square roots are allowed and give a negative result
	Negative numbers are shown by a "-" in the far left (ninth) digit thereby allowing full eight digit negative numbers.
	The percentage just divides by 100, repeatedly
	It suffers the zero root bug. If you perform a square root of zero after another square root, the answer inherits the number of decimal places. i.e. key in (2)(.)(2)(5)(SQRT) to give “1.5” now key in (0)(SQRT) to give “0.0”. Interestingly, if you try to key in more numbers then they fill from the far right!