1. At first sight this is a pretty uninteresting rule with a basic Mannheim configuration. When I got back home I wondered why I'd bought it - particularly since there is no indication of the manufacturer.  Then I started to look a bit more carefully.

2. The lettering, for example the rather ornate p symbol shown below, suggests an early 20th century date of construction.

3. The only information on the rule is the patent number, DR Patent 173660. This, according to Peter Hopp, is a Nestler patent of 1905. About the time that I was scanning this, Peter Holland posted a message to the slide rule group mentioning a Swiss site with almost all patents ever issued at:

http://ch.espacenet.com/espacenet/ch/en/e_net.htm

I decided to have a look at the patent. You can see part of it below. The patent was actually applied for on 26 April 1905 and granted on 27 July 1906.

4. The patent also had a drawing of the rule. I repeat part of this below. As can been the drawing shows the scales being fixed in place with screws - exactly as on this rule.

5. Another interesting feature on this rule is the slots in the well of the rule to improve flexibility.

6. There is also an inch scale in the well of the rule to enable distances up to 21" to be measured. This shows that the rule was destined for the British (or US) market.