Here’s a reproduction copy of Eastman Kodak’s instructions for the Cirkut No. 6 Outfit.

My Cirkut No. 6 has the standard doublet 8″/14″lens as shown below.
I always used the 8″ lens. Following the instructions on page 5-6 of the instruction manual (above), I would set the front of the camera so the small brass marker was across from the “D” marker on the camera bed.
I would then focus the camera carefully on the ground glass. On the other side of the front camera bed, the scale for the 8″ lens would indicate the gear I should use, as shown below.
In most cases, focus is at or near infinity, in which case I would use the “50” gear as shown below.

Hopefully this is of some help if you acquired one of these marvellous cameras.