Delved a bit more into this & it would appear that the psychrometer was on both sides.
(So two " The first, a dry bulb thermometer, is used to measure the temperature by being exposed to the air. The second, a wet bulb thermometer, measures temperature by having the bulb dipped in a liquid")
Also this was a joint US/UK operation, using these aircraft from 25 BG.
B-17 Flying Fortress of the 25th Bomb Group.
'Back Row- Left to Right Edward Corner Tail Gunner (Deceased)- Sam Odensky RDG- Donald Yennie Engineer (Status Unknown) The Hawk RAF) 1st Row Kneeling L to R Warren Forgie (Pilot), Earnest York (Co-Pilot), Edward Sofranko (Navigator), Robert Poe (Ball Gunner) (Edward York Died Oct 15, 1988 Heart Attack)
Sergeant W.H. Timms of the RAF and Captain A.E. Podjowski of the USAAF fit a psychrometer to a USAAF aircraft before a weather mission 17 February 1944.
B-17's were not the only ones fitted with this mod it appears?
The nose of a B-24 Liberator of the 25th Bomb Group, fitted with weather equipment. Handwritten on reverse: '28/8/44.