Prototype visibility meter, circa 1911
1911
Visibility meter
circa 1941
Visibility Meter Mark IB, 1942
1942
Visibility meter MkII by Casella London
1943
Beutell visibility meter, 1943.
1949
Bennett-Casella visibility meter by C.F. Casella and Co. Ltd
1949
Visibility Meter, 1930-1935
1930-1935