The Exposure tables are grouped in to three: Bromide papers; Gaslight papers and Lantern plates. For each group a grid shows the exposure time based on the measured density (0 - 30) and the brand of paper or plate. The grid is applicable for a specified type of light and distance of the light from the printing frame.

A very popular density meter, the original model was brought out in 1911. The improved model of c.1928 had an opal diffuser above the negative and in c.1930 a focusing eyepiece was added. Produced in two sizes, No. 1 - for half-plates and No. 2 for whole-plates. The No. 2 was added shortly after the smaller size. Early illustrations do not show the retaining spring for the negative. Instructions from around 1930 state that the opal diffuser was a suggestion by W.B. Ferguson.

The meter consists of a shallow box with two holes in its top. Below each hole is a mirror that reflects into the eyepiece, the mirror below the 'negative' hole only reflects half of the field so that the eyepiece shows a split field of the comparison wedge and the negative. The density wedge fits into a slot at the lower end of the meter and covers the lower of the holes. The negative is placed on the meter and the part of the negative to be measured is arranged to be over the hole nearer to the eyepiece. The density wedge is now moved so that both halves of the field show a common density, the density can then be read from a scale on the wedge. The exposure time for a print is calculated by measuring the densest part of the negative that is to show detail. Tables or a calculator give the exposure time based on the negative density, distance from the light source and type of paper. By measuring the high and low densities the type of paper to be used can be found.

According to advertisements its main function was in bromide printing but it could also be used to find the speed of papers and light strength. The meter has first to be calibrated to the particular set-up in the darkroom (lighting etc). The numbers on the wedge correspond to those used by Hurter & Driffield e.g. 10 on the wedge corresponds to 1.0 H & D Density and passes 1/10th of the incident light. Normally a 6 ½" wedge is supplied, the 10" was for 'research' work and probably introduced in the mid 1930s. A supplementary wedge was also available to be used in conjunction with the ordinary to read higher densities.

Mainly used to determine the correct exposure for bromide prints. Light passes through the negative onto a screen, this is compared to light from the same source but not passing through the negative. The light not passing through the negative is adjusted by a series of wheel stops until it is the same brightness as that passing through the negative. The density number (wheel stop) and type of paper shown in a table give the exposure time. The patent talks of adjusting the colour of the light.

These were used in various light measuring devices, Abney describes a sensitometer by Warnerke fitted with a similar wedge.