1. Dennart and Pape were the company who eventually produced the "Aristo" brand of slide rules.

2. This rule is interesting in that it has two slides. One them is the normal slide found in Mannhein rules of the period with B and C scales on the front and sine, log and tangent scales on the back. The second has log-log scales. One one face there are two scales, labelled E, covering the range 1.07 to 2.0 and 2.0 to 1000. On the other face, labelled -E, they run from .001 to 0.5 and 0.5 to 0.934.

3. The rule is covered by patent number DRP 124,499, which according to Peter Hopp (Slide Rules their History, Models and Makers, p 280) is for the use of "metal or other flexible bottom to join the two halves of the stock". It is rather surprising that the method of presenting the log-log scales was not covered by a patent. This patent was dated 1901.

4. The rule is the same as the one described by C N Pickworth (The Slide Rule, 16 th edition 1919) which he refers to as the Davis Log-log rule. The rule described is identical to the one pictured below and since Davis was known to import D&P rules this fact is not surprising. It is pure speculation but Pickworth was closely associated with Faber Castell, another German company; could it be that he failed to mention the maker of the "Davis" rule for professional reasons?

My thanks to Mark Butterworth for providing the images of this rule. His web site is at http://www.priscus.co.uk .