The Weston Master IV

The fourth of the Weston Master series, this meter was being produced in 1960 in Enfield, Middlesex for the US and UK markets where for the latter it was also distributed by Ilford Ltd. It is a complete re-design, in an aluminium and plastic case, smaller and lighter than the Model III. It had greatly improved sensitivity, a better designed scale, a larger dial and a sliding needle lock. A great example of British design and engineering. These were the first to use the newly introduced "exposure values" and ASA/DIN ratings instead of Weston speeds, which is why they are probably the oldest of the Master series that are still in active use. of ASA speeds up to 1600, LVs 1-18, stops f1-32 and speeds 64-1/1000 sec. 

The photos show UK model no S461-4 serial 004KK.

I've had this from new, it works perfectly and always has. It is the most reliable and accurate piece of equipment I have ever come across and has been with me on hunderds of professional shoots. There is really no need to go to a V or Euromaster - they don't have anything over a IV.

The instruction book text is here.

In the US it was imported from the UK under the brand Daystrom Incorporated - Weston Instruments Division.

The SER.W variant of this model was made in Japan - under licence by Sekonic and either branded a Sekonic L104 or as the Weston IV but still bear the Daystrom Inc label. (Thanks to Franco Terlizzese from Italy for this latter information.)