I started collecting mechanical calculators almost by accident- I just came across one on EBay one day whilst looking for Fowlers, thought it might be interesting, put a small bid on it and won it. I soon came across a couple more and then found that there were quite a number of varieties after a bit of research on the web.
My collection is limited to two basic types for space reasons. These are slide adders, sometimes called troncets or addiators after early models, and dial adders, characterised by the Addometer. However I have not separated these two types in the pages that follow but have categorised the calculators by maker or country of origin.

When looking at the slide adders it will be seen that there are three basic types. The first type, typified by the early Addiator models, is double sided with addition on the front side and subtraction on the reverse. The second has addition and subtraction sections on the same side, typified by the Produx. The third has just one section for both addition and subtraction and different rules have to be followed for the two processes. To make it simpler some of these have a flip over front panel or a sliding cover. Multiplication and division are carried out by processes involving multiple addition or subtraction.