What is this thing I have found in the loft.

It is in a old leather case, all lined with purple velvet.   It says on it Weston Master 111.   Universal Exposure Meter.  It has a red needle which must go up from 25 to 1600.  Below that it has  that looks a bit like an old fashioned timer for turning your light on.  In the middle of that it says Exposure Value.  On the back of the gadget it says Distributed by Sangamo Weston, Ilford.     Any info, please, ?  Mrs Bouquet

Sorry to inform you you cannot sell it and use the proceeds to go on a cruise !
They sell at about £3 on ebay !