Imperial Exposure Reckoner ~ 1907

Below are two version of the 1907 Imperial Exposure Reckoner. The top one is the earlier, evidenced by the lower speed range of film, running from 6 to 400 H&D (Hurter & Driffield) and the exposure time range being marked in seconds, minutes and also hours !

The second version, shown below the first, has a film speed range 5 to 600 H&D. The exposure time is only marked as seconds and minutes. There is also additional information and the Reckoner has an overall 'cleaner' (more modern looking) layout.

Early version.

Early version,

folding cover.

Later version