Me too. But it's a good'n!
This is a 10-inch Keuffel & Esser Log Log Decitrig Duplex Model 4081-3, S/N 867525, made of pure mahogany plated in white celluloid, with a glass indicator held together with plastic and metal screws, inside the classic sewn orange leather case. The Model 4081-3's were only made from 1938 to 1947. The patent on the metal clip on the flap loop on the case (2,000,337) is from 1935, the latest patent (2,170,144) on the rule itself is from 1939 and the 'PAT. PEND.' after that most likely refers to their next patent in sequence (2,285,722), granted June 9, 1942, leading me to believe mine is from 1940-1941.
A very handy K&E dating timeline can be found on the
Slide Rule Museum site, also directly linked
here.
Also good info posted on the McCoy's catalog collector's site
here.