Maker's Name: 
Edwards High Vacuum Ltd.

The McLeod gauge is used to measure vacuum pressure accurately down to 1/10000 millimetre of Mercury. In principle, a sample of gas, the pressure of which is to be measured, is compressed from a large bulb of known volume, into a capillary tube of known volume, the pressure required to do this being measured (in millimetres of Mercury). With the volumes and the capillary pressure known, a simple formula gives the actual pressure of the original gas. This small version could be read down to about 0.001 torr (not accounting for the mercury vapour it introduces as that condenses in the capillary).

The mercury has been removed.