GEM Chain Adders - Francis WEB

The most common within the chain type adding machines, and maybe the cheaper too, was the GEM. This model was patented in 1907 and sold easily in the US with a price of $10. Well constructed little machines, and easy to operate, as the carry over was automatic. You simply have to enter the number you want to add. The regular Adders were not carrying over.
They came in several types, wiith 7 8 or 9 columns. I saw a mention of some models with non-decimal scales, such as inches or feet.
The ones in my collection are simple 7 column model, but still works very well, after over a century.
Here is anoverview on how to operate:

Using a stylus or pen, push the numbers you want to select down. In the example above, I select 6 and I push it down all the way to the bottom.

Example of an addition, first number entered : 56

Second number added : 65. The result is given : 121. The carry over of the hundreds was automatic


To reset all numbers to zero, rotate the knob on the bottom right.

Here are a couple of short videos to show how to use this device and different versions of it.