# Jaap's Mechanical Calculators Page

Video
Patents

There are four number wheels which the user can adjust using the stylus provided with the machine. To the top-right of each wheel is a small square window showing a single digit. Each wheel has ten holes arranged around its rim into which the stylus can be put, and these are lined up with the digits 0 to 9 that are printed on the case next to the holes. To add a number, enter the digits one at a time simply by putting the stylus in the hole next to the digit you want to add and turning the wheel clockwise until the stylus hits the tab by the digit zero. When a wheel is turned from 9 to 0, a carry to the next wheel is performed automatically.

This adding machine cannot easily do subtraction. The carry mechanism does not work in reverse, so if you turn a wheel in the opposite direction and its value goes below 0 to become 9, the digit to the left will not be decremented. You can of course perform a subtraction by adding the tens complement of the number you want to subtract, but there are no markings on the machine to help you with that.

There is no clearing mechanism. To clear, you have to subtract the value of each digit so that it becomes 0. To help with this, there is a marking next to one of the holes of each wheel and you simply put your stylus in the marked hole and rotate anticlockwise until the stylus hits the tab.

The adding machine is built into a nice metal box, a bit like a cigarette case. It comes with a stylus which can be stored inside the box, in an indentation above the display windows. On the inside of the lid there used to be a "Magic Slate". This is a plastic sheet that you can draw or write on using the stylus, and clear again by lifting up the sheet off its backing. My Ken+Add is missing its magic slate and instruction sheet.

The mechanism is very simple, and virtually identical to that of the Lightning Calculator, later called the Lightning Adding Machine. This same mechanism was also used in the Purse Adding Machine, though the Kes+Add is much sturdier and much higher quality.

The Ken+Add was designed by Kenneth R. Pangburn in or before 1949 and went into production in 1950. It should not be confused with the KesAdd which is a similar adder that is also named after its designer. The KesAdd had a more original mechanism, designed around the same time, but marketed a few years later.

There are two versions of the Ken+Add. The first version was made from 1950 till 1954 or 1955. It has a cylindrical stylus, stored in a deep slot in the inner casing. The inner casing also has rounded edges around the windows and number wheels, and is two-coloured - silver along the top around the stylus slot, and green around the windows and wheels. The writing says "Ken+Add Machines Co., Duluth, Minn., U.S.A., Pat. applied for".

My Ken+Add is of the second type, which was in production from about 1955 or 1956. The inner casing is much flatter, with the window edges much shallower and less rounded. The stylus slot is also a very shallow, so the stylus is made of an almost flat piece of metal instead of a cylindrical rod. The inner case is all green, and the writing says "Ken+Add Machines Co., St. Paul, Minn., U.S.A., Pat. applied for". It is clear that the changes made this version cheaper and easier to manufacture. It was on the market until at least 1958, but I do not know when that ended.

## Video

Here are the advertisements I found. There are very few of the second generation Ken+Add, though it is likely to have sold through stationers and department stores for several years.

## Patents

The mechanism of the Ken+Add is clearly not original enough to be patented, but there are two design patents. The only other patents that Kenneth Pangburn was granted are for tape dispensers and tape applicators (USD 179,091 S, US 2,560,241).

PatentFiling datePublish dateNameDescription
USD 163,135 S10-10-194901-05-1951Kenneth R. PangburnPocket Adding Apparatus
USD 163,136 S01-05-195001-05-1951Kenneth R. PangburnPocket Adding Apparatus Unit