In use a table showing the month and time of day provides a light value (A - J). On the first slide of the calculator the sky condition is aligned with the A - J value. On the second slide the plate speed is aligned to the subject. The shutter speed / aperture pairs can then be read. There is also a scale for flashlight work showing distance and giving grains of flash powder to be used rather than shutter speed.

A separate calculator is used for development: the plate class (A - E) is set against the subject type. The development time is then shown for different temperatures. Two scales are shown for tank or dish work.

The scales were arranged by P.H. Dawson. The price was 1/-.

A table is used to provide a light value index based on time of day, month and sky conditions. This is adjusted for the type of subject. A ribbon is moved to align the light value index to the plate speed in use (shown by colour of label on the box). The shutter speed / aperture pairs can then be read. The meter card is contained in an envelope which includes a plate speed conversion table.

A simple cardboard calculator produced for a number of years. Variations have Scheiner plate speeds. In use the hour is set against the month. The plate speed then points to a light value. The subject is aligned to the light value. The shutter speed / aperture pairs can then be read.