Vickers Victoria IIIs J7929 and J7928 of No 216 Sqn in the Middle East circa 1926. The forward fuselage of the furthest machine is inscribed with a circular series of numbers from 0 to 3 and what appears to be a rotating pointer. What did it represent and what was it used for?

A rod with an upturned end beneath the tail of a Vickers Virginia Mk X, evidently being used for experimental work at Boscombe Down circa 1934.