The fourth of the Weston Master series, this meter was being produced in 1960 in Newark NJ by Sangamo Weston and in Enfield, Middlesex for the UK market where it was also distribued by Ilford Ltd.
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. 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.
This model was also made in Japan - under licence by Sekonic and either branded a Sekonic L104 or as the Weston IV (Thanks to Franco Terlizzese from Italy for this latter information.)
