The Weston Master was based on the 650 Universal meter but is thinner and more streamlined than the earlier model. It appeared first in the USA in 1939, following the war (1947) production was started in Britain to avoid import difficulties. The Enfield models have white faces those made in the USA at the time have black. In 1951 Sangamo Weston introduced the model II which was already available from 1946 in the USA. An 'Invercone' became available for incident light measurement. The model III appeared in Britain in 1957. This had a dial that was easier to read and an Exposure Value (EV) scale. The Weston speed ratings were re-aligned to correspond to ASA. In 1961 the model IV appeared, this had a satin chrome finish rather than the black paint of the earlier models. A lock for the needle was added and the scale was made clearer by omitting some values.

In use the film speed is set in a window on the centre dial. The reading is taken, an index is set against the value of the reading on the outer dial of the calculator. The shutter speed and aperture pairs can then be read. There are index lines for: normal, U - shadow readings, O - highlight readings, A - half exposure, C - double exposure. The Euromaster also had indices for two stops extra exposure, three stops extra and two stops less. The dials of early models are very full and difficult to read.

The U and O indices are separated by a brightness range of 128:1 which approximates to the latitude of the film then in use. Taking a reading of the shadow area of the subject and using the U index would ensure that the shadows were correctly exposed though highlight detail may be lost. Similarly if highlight detail was more important a reading of the highlights would be taken and set against the O index.

Prices:

• Model I £9.15.0
• Model II £11.5.0
• Model III £10.18.3