affect the base instruments. The results obtained using the leapfrog method are more accurate than those obtained using
the single-base method, and compare favorably with the two-base method results.
16.
Optimum Accuracy Considerations
In order to insure the most accurate results regardless of the altimetry method employed, certain general
considerations, corrections, and conditions should be observed. These are as follows:
a. The accuracy of altimeter work is directly connected to the stability of the prevailing weather conditions.
Values recorded when weather conditions are unstable are usually so erratic as to constitute a waste of time. Wind
velocities are usually an excellent guide to follow in determining whether scheduled operations are to be conducted. In
general, the most favorable results are obtained with winds up to 10 miles per hour. However, reasonably favorable
results are possible with winds up to 15 miles per hour. When the wind velocity exceeds 15 miles per hour, operations
should be cancelled. In general, the early morning hours between six and nine o'clock, and the early evening hours
between four and eight o'clock afford the most stable pressure conditions. However, excellent results have been obtained
up to midnight and later.
b. Prior to a scheduled operation, all altimeters in the set to be used must be calibrated, and a calibration
correction factor must be determined for each instrument. This is accomplished using the following procedure:
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