# Jaap's Mechanical Calculators Page

The O.J. Adder is a sturdy dial adder for British currency, probably made in about 1960. It has a heavy case of cast iron, presenting a face with four dials angled towards the user. On the right hand side is a holder containing a plastic stylus.

The rightmost dial is a disc with 12 holes and registers the pence amount. It has 12 holes near the rim labelled 0 to 11, and to add some number of pennies you put the stylus in the appropriate hole and turn the dial until the stylus hits a metal stopping par at the bottom. The total pence amount can be read through another hole inside the dial. If the dial completes a revolution, the next dial is automatically moved one step. That next dial registers shillings, and has 20 holes labelled 0 to 19. The dial to the left of that counts pounds, and also has 20 holes. The last dial is a simple pointer, that counts up to 1000 pounds in multiples of 20.

There is no clearing mechanism. Each disc dial has an arrow pointing to one hole. To reset the dials go from right to left, adding the amount indicated by the arrows. Finally twist the left pointer to zero by hand.

The adder does not have a serial number. The adder has a stored energy carry mechanism. As a dial turns, pins push up a lever against a spring, and then lets the lever drop down again. That lever has a pawl attached so that when it drops the next wheel is shifted one step.

I do not have the original instruction leaflet, but I found photos online and the text is as follows:

 INSTRUCTIONS FOR USING THE O. J. ADDER The essence of the O. J. Adder is that good results are obtained from the ﬁrst, although practice naturally increases the operator's speed. The machine must be set to zero before use. Insert the stylus in the hole marked with an arrow on the PENCE DIAL and rotate the dial clockwise until the stylus meets the stop, when the red 0 shows in the small window in the dial. Repeat this process with the SHILLINGS DIAL, then the POUNDS DIAL and
 finally turn the knob of the POUNDS POINTER clockwise until the pointer points to 0. The machine is now ready for use. This order of dialling is only necessary for setting the machine to zero. When adding, the dials can be used in any convenient order. 1 12 6 2 7 3 19 18 4 1 10 9 -------- £25 8 10 --------- After adding these ﬁgures, it will be seen that the POUNDS POINTER indi- cates £20, the POUNDS DIAL shows £5, the SHILLINGS DIAL 8/- and the PENCE DIAL 10d.
Some users prefer to add each line separately, while others prefer to add in columns, either from left to right, or from right to left.
Except when setting to zero, it does not matter in what order the dials are used.
At the beginning of an addition, always see that the machine shows zero throughout.

Sold by:
 THE OJ. ADDER Guarantee Should any defect of material or workmanship become apparent within six months of the date of purchase, we undertake to make good the defect at our own expense, and refund the postage, provided that the machine is returned to us postage paid, and securely packed in the box supplied with the machine. The above guarantee is not operative until the attached post card has been filled in, and returned to us. HOLMAN ENGINEERING WORKS Holman Street Kidderminster

## Video

Here is a video where I demonstrate the O.J. Adder.

## History

The O.J. Adder was invented by Oscar Styles Penn (1890-1961). As a young man he had an interest in aviaton and was involved in building and testing the Newington monoplane in Hull. In the first world war he enlisted, joining the Motor Machine Gun Service, and rose to the rank of captain. After the war, he worked at Roadless Traction Ltd. This company was founded in 1919 by Colonel Phillip Henry Johnson, and a few other army officers including Penn. Johnson worked on the development of the military tank in what became the Tank Corps, but I have not been able to confirm whether Penn and the other officers worked there together, but it seems likely. Johnson had been allowed to keep patents on his work in caterpillar tracks, and the company was to commercially develop that.

By 1943 Oscar Penn worked at Aveling-Barford in Grantham, becoming their chief engineer. Amongst many other things, he developed the "calfdozer", a very small bulldozer. After he retired, he lived in Callow Hill, near Kidderminster, where he continued inventing and set up Penn Inventions Ltd in 1955 to commercialize them.

## Patents

Oscar Styles Penn has a large number of patents with Roadless Traction related to caterpillar tracks, one for a valve for inflatable liferafts (GB 535,467) which went to the Walter Kidde Company Ltd., and many with Aveling Barford related to machines used in construction such as the calfdozer (GB 575,334). After the adder he patented a rise chair for the elderly (GB 949,995).

PatentFiling datePublish dateNameDescription
GB 880,60827-11-195825-10-1961Oscar Styles Penn Penn Inventions LtdAdding Machine