or Wallace and Tiernan Form 1851, or equivalent. may be used (fig. 6). When making and recording observations, if
there is any difference in elevation between the point for which an observation is desired, and the point where the
instrument was actually read, the difference in elevation should be determined by direct measurement using a tape or
similar device. This measured difference in elevation is not set down in the field notes. Instead, the difference is noted -
Figure 6. Wallace & Tiernan Form 1851.
with the appropriate algebraic sign as a correction to the altitude reading of the point actually observed in order to record
the "FIELD ALTIMETER READINGS" of the desired point. If the observed point is lower than the desired point, the
correction is plus (+), and if higher than the desired point, is minus (-).
After the field run has been , completed, the field notes are used to make the final computation. To make the
final computation, a form similar to the one shown in figure 7 may be used. Computations are made in accordance with
the following procedure: