Litton Monroe 30

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Calculators: Handheld: Litton Monroe 30

		Size (approx):	89mm x 152mm x 32-51mm (w,h,d) Weight 236g excluding batteries
		Power:	6V DC using 4 x AA size batteries. It accepts an adapter/charger (9V 1.4W) through a three-pin (with earth tag) socket on the rear side to the top left under the display. The battery compartment has an odd locking mechanism – the top two feet slide up to open the cover. The whole of the inside of the battery compartment is removable in order to allow the insertion of a rechargeable pack. Quoted battery life for Alkaline is 20 hours, Nickel Cadmium is 11 hours fully charged. Charge time is quoted at 12 to 14 hours.
		Case:	Two piece matt plastic case in rather a strange shape and dull colour scheme. The lower section is beige and U-shaped in both directions. The upper section in brown with a pronounced raised section around the display. A raised panel on the front holds the switch and a recess for a brown printed metallic sticker with the brand and model number. A flat and tilted orange plastic filter gives a large clear display. The large bevelled keys are springy and slightly hollow sounding, more like the older desktops. A large metallic sticker on the rear is printed black with specifications.
		Display:	8 digit orange Panaplex gas discharge display with a ninth digit for negative and error indicators.
		Features:	Standard four functions and percentages. Reverse Polish Notation (RPN) logic.
		Age:	1973/4
		Manufacturer:	Litton Monroe, The Calculator Company. A division of the Litton Business Systems Inc, Litton Industries. Made in the USA. Serial number E225985.
		Comments:	Very unusually chunky calculator which is rather a dull colour but makes up for it with the lovely large Panaplex display. Unfortunately my example has its rear sticker quite worn so it is difficult to read the company information. RPN takes a little getting used to but otherwise the logic is goof. Original case is soft brown plastic with side, top, half-side zip. It has an inner cloth lining and gold lettering on the front saying Litton Monroe that has nearly worn off.

Components:	Main board: Cannot get access! Secondary board: 5 x transistors 18 x diodes 5 x capacitors 13 x resistors 1 x transformer: 1408P 3B7 (possibly February 1973 date code)
Boards:	The secondary (power supply?) board sits on top of the main cpu/display board and is connected via 11 copper solder tags and separated by foam spacers. The latter has a metal bracket for the case screws and a metal panel for either shielding or support. The main board is fixed to the front with five screws, one of which is very inaccessible without the correct tool.
Construction:	Remove the two screws that are under the rubber feet. You will find that the rubber feet will pop out if carefully prized as they are not glued in. The back section will then lift off easily if hinged from the top.

Logic comments:	(C/CE) is used once to cancel the last number entered and a second press clears the whole calculator.
	Input overflow is suppressed, inputting a ninth digit is ignored
	Negative numbers are shown with a minus sign in the far left (ninth) digit thereby allowing full 8 digit negative numbers.
	It operates with RPN; i.e. 4-6 is input at (4)(+)(6)(-) with no need for equals key as this is only used on multiply and divide.
	There is automatic constant on multiple and divide only
	Divide by zero shows "C” in the far left (ninth) digit and is recoverable using (C/CE)
	Overflow shows the result and “C” (or “E” if negative) in the far left (ninth) digit and is recoverable using (C/CE)
	The on/off switch has two on positions. The “F” position is for full floating point operation and the “+” position is for fixed two decimal financial input. In the latter mode entering (1)(2)(3) result in the number “1.23”


The manual measures 127mm by 77m and is 24 pages thick. In English only it has in-depth specifications and examples. © 1994, printed in the USA, Ref. 1743-S.		This example page shows how the battery compartment is opened and how you remove the inner plastic battery module to install the rechargeable pack.

	The scan on the left shows the calculator with the rear section removed. You can see the secondary (mostly power supply) board sitting on top of the main cpu/keyboard board. There is an additional screw to the right that is very difficult to access. The two boards are separated by pieces of foam and connected via copper tag-posts. Expensive to make and construct. Notice the metal bracket and panel in the lower section - again no expense spared in the construction of this early handheld calculator. Just below midway you can see the three copper pillars that connect to the battery module. At the top right you can see the mains adapter connectors on the secondary board.