1. Although I have included this rule in the non-standard section, it is a fairly basic standard rule except that it is made of cardboard. It has a very simple cursor which, as far as I can tell, has never had a spring even though it is very loose.
2. I do in fact have two almost identical rules, the differences being that one one of them has tables of fairly conventional constants on the back and it also has written on it markings related to house and plot area in  thousands of square feet. The rule also has a "gauge mark" for use with these extra marking.
3. The person who added these marking has also developed his own rule specifically for this type of problem which he refers to as a town planning rule. This rule is shown below. Not only has he marked it with his name and the word "copyright" he has also got someone to sign across it and to date it, that date being 22^nd May 1925. The person who countersigned it gives his trade as "mason" suggesting that the person who designed the rule was perhaps an architect who got a professional colleague to sign it for him.
4. I also have another rule, for pipe design, apparently owned by the same person who also designed rules for this purpose. This rule can seen here. As far as I know neither of the rules designed by Ronald W. North was ever produced so it is quite a fitting memorial to him that his rules now should be available for inspection all over the world via the internet.

Front view

Detail - front left

Detail - back