ID: 
1019
Maker's Name: 
Griffin
Where made: 
England
Dimensions: 
3.7 × 3.7 × 21 cm

The unit is a U-tube filled with Mercury. Application of pressure or vacuum in one arm lowers or raises the column on that side. The pressure or vacuum is shown as the difference in levels between the two columns ie as so many millimetres of Mercury difference. One atmosphere of pressure is equivalent to 100 kiloPascals, or 14.7 pounds per square inch, or 760 millimetres column height of Mercury.