1. This rule was very cheaply made but has still maintained its
accuracy and the slide moves smoothly.
2. One feature which I first noticed on this rule (trying to find something good to say
about the Lawrence) but I now realise is common is the table of approximations on
the back. For example the ratio of the circumference to diameter of a circle is given as
710/226. This is equal to 3.14159292. The true value of pi is 3.14159254. An accuracy of
1:12 000 000. It was also noticeable that they optimised space by giving less familiar
units, e.g. centimetre, in full, but more familiar ones abbreviated, e.g. in. for inch.
Unfortunately what would otherwise have been a useful table is marred by some typos! I
give below a more detailed table. This table was probably copied from Faber Castell
rules. See the Faber Castell 360 for details.
3. Although placed in the 10" rules it was actually about 8" long.
4. The Hemmi 40 RK has a correct version of the tables and
the Keuffel and Esser 4058W uses a similar method but with
some different settings.
