Five-inch version of Versatrig.
Custom made by Hemmi for Frederick Post and Hughes-Owens; no Hemmi model number exists for this model.

I can find no Frederick Post, Teledyne-Post or Hughes-Owens catalog that lists this slide rule.  None.  Most specimens have date code "SF" (June 1968).   Jodie S Hobson has one with date code "SA;"  Warren Salomon owns a"TE" (May 1969)  Hughes-Owens Pocket Versatrig.