(1) A suggested method of calibration is by use of the W & T Portable Test Kit FU2904. This kit consists of
a hand pump with connecting tubing permitting simultaneous calibration of up to six altimeters. The
connection to the altimeter is made at the vent tube (10, fig. 5).
(2) Exert vacuum or pressure to run the altimeters through full range making comparison readings, using
one altimeter as a standard, and noting the differences at each 50 meter scale division for each
altimeter, charting these differences for later use.
Note. If more than 6 altimeters are to be calibrated, use the same altimeter as a standard.
(3) It is advisable to make a new set of comparison readings at least every three months, or when
instruments have been shipped over long distances, severely jarred, or when an instrument is to be used
with a group with which it has not been previously calibrated.
Caution: Once an altimeter has been calibrated, do not move the adjusting screw unless it is
to be recalibrated.
c. Prior to the start of the actual recording run, all observers should set their watches in common agreement. A
check of all watches should be made at the completion of the run to determine whether time corrections need be applied
to the field readings. Watches obviously erratic or unreliable must not be used.