In measuring heights with the Aneroid care should be taken that the instrument is not influenced by the heat of the hand nor by the direct rays from the sun.
The instrument should always be tapped gently with the finger at the moment of taking an observation. It should also be held in the same position for both observations; preferably with the face horizontal.
Considerable care is also required to determine exactly where the index points. It is best accomplished by sighting along the pointer, using one eye only for the purpose.
The following example will illustrate the use of the tables.
| Barometer at Station A | 30.04 | Thermometer 78° |
| ” ” ” B | 28.68 | ” 65° |
From [Table I] we find height corresponding to reading at A is 857 feet. The height for B is 2120 feet.
The approximate height is 2120-857 = 1263 feet; but the sum of the temperatures is 143°. An additional correction of
is, therefore, to be applied to the above difference; this is 54 feet. The total estimated difference of altitude is then 1263 + 54 = 1317 feet.
The formula directly applied is