1. This is an example of evolution of rules with similar model numbers, in this case 30 years apart.
2. One obvious difference is that the early rule uses only black ink.
3. The cursor has also developed - in the early model screws are used - the later model is one-piece
4. The only difference in scales is that the later model has a CI scale. Though none of the scales are named (apart from the trig and log scales) on either model.
5. Both rules are made of laminated wood construction with plastic scales. They also both have metal strips running through the stock and slide. One slight difference is that in the early rule the slide has a small strip at right angle to the slide and the later on has a larger strip parallel to the slide.
6. The later rule has dropped the use of Quot.+1 and Prod.-1 to aid placing of decimal point.
7. Rather surprisingly perhaps, the rules have identical tables of constants on the back. One of the tables give values of factors which can used with C and D scales to get constants to a high degrees of accuracy.
8. The same table, with several errors, appears on the cheap Lawrence rule made in the US. The Hemmi 40RK uses an identical scale and the Keuffel and Esser 4058W uses a similar technique but with some different settings.