This is a very simple and very early actinometer that pre-dates the Watkins Standard. A roll of paper made sensitive by bromine is wound inside a small shallow cylinder. The paper is pulled into a flat box attached to the cylinder, this has a cover glass under which the paper is exposed. A companion tint surrounds the exposing aperture. The patent was issued in conjunction with W.L. Sarjeant. The meter was also produced in boxwood.

A separate calculator would have been used to work out the exposure.