Unusual Mystery Desk Barometer

An unusual early 20^th Century German precision aneroid desk barometer.  Brass base housing the mechanism supporting the barometer dial.  Slender wire and chain attached to the indicator.  The signed glass dial in English on the back glass and marked "Atmospheric Pressure relative to Sea-Level".  White arrow indicator formed so that its pointer is close to the index.  Small brass knob in the centre to allow the current reading to be recorded by a second arrow pointer.   Retailers mark engraved on th front of the base "Optician - JB Watson  Edinburgh"