Casella CEL Fortin barometer - Manual (Page 6)

HB3121
6
If the readings are to be corrected to mean sea level, the height of the cistern
should be accurately found and recorded as the station height. That this is
important will be realised from the fact that a difference of 30cm equals a change
in barometric height of 0.025mm (0.3mb).
POINT ZERO
ADJUSTING
SCREW
TUBE
MERCURY
Cut away diagram of the Cistern