(4) Follow the computation key provided in each of the blocks on the form to complete the calculation.
Figure 9. Wallace & Tiernan Form 1925.
(5) The adjustment of the computed altimeter elevations depends largely upon the observations made with
the roving altimeters at benchmarks and other known points of elevation. These observations are
known as check or tie points. A minimum of two such points is desirable and more should be obtained,
if possible. If only two check points are used, the observer can make an error at one of them,
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