Interesting Antique / Vintage ' VACUSTAT ' by W. EDWARDS of LONDON

I have no idea at all what this early Scientific Testing Instrument is ??? ... I am therefore offering as for Spares or Restoration as I cannot state if its complete and working ? ... I can see Mercury in the Tubes and all the Tubes appear intact.

It states ' VACUSTAT (MODEL 2E) W. EDWARDS & CO LONDON LTD '.. LOWER SYDENHAM.

Its Metal face with glazed insert measures 7 1/2 ins diameter and weighs 4 Kilos unpacked.