Altimeter, US Navy No 701, Tyco, 12,000FT, WWI-Post WW1 era PB-1 The knob rotates the pointer

The knob rotates the pointer along its axis to select the desired course heading marked along the perimeter scale

This would be used to set up a carpet bombing run

See photos in the gallery describing the system in greater detail

The knob at the bottom is used to adjust variation

such as torpedo bomber TBM Avenger (see image from TBM Flight Manual)

Altimeter, US Navy No 701, Tyco, 12,000FT, WWI-Post WW1 era PB-1 The knob rotates the pointerThis is an Altimeter used in military aircraft of the US Navy either during or post WW1. This altimeter crudely measured altitude from 0 12,000 ft. By gripping the knurled rim of the faceplate and turning, the numerical scale rotates clockwise or counter clockwise while the pointer remains stationary, to correct the altitude reading as required. May have been used in an airship of the US Navy. This looks very similar to the altimeter depicted in the