The Burroughs patents (1,016,501 and 1,023,168) covering their first calculator were issued in early 1912 (note: NOT "adding machine"). While its obvious that the case design was a copy of the shoebox Comptometer, it embodied some rather unqiue features not found on the F&T machine.
The most noticable is the forward positioning and single-throw action of the clearing handle, something that the Comptometer lacked for another 8 years. It also weighed less at 13 lbs for their 9-column version compared to 17 lbs for an 8-column Compt.
The machine lacked the Compt's "subtraction cutoff" (or "carry inhibit") tabs but included an extra key (next to the 9-key of the high order column) which added 9 to any "hanging one" in the high order register dial. Strangely, its keystems were vertically oriented unlike either Compts OR its own successor models.
As noted elsewhere, this "shoebox" shape was shortly replaced by a model with rounded corners which was produced for some 50 years and shared the market for key-driven calcs with the Comptometer thereafter.