This is one of the simplest extinction meters and, reportedly, quite accurate. In early models the number just visible in the 'finder' is aligned with a box depicting the light conditions and subject. The shutter speed / aperture pairs can then be read. This was accurate for one film speed only. If a different speed was used adjustment was made after lining up the subject box and number. On later models a table gave an index for the film speed this was combined with the light value number e.g. index = C, number = 8, gives C8 which is then aligned with the subject box. The drawings in the subject boxes differ between examples. The price was 5/- in 1939. A cine model was also produced c.1936.