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How to Determine Daily Rates
Figure 5-6. Excerpt from the Timepiece Rate Book.
Average Daily
Rate (ADR)
Example: a chronometer whose rate is +1.5 seconds will gain 1.5 seconds
every 24 hours. Chronometer rate is usually expressed as seconds and
tenths of seconds per day and is labeled gaining or losing. Chronometer
rate is determined by comparing errors obtained several days apart and
dividing the difference by the number of days between readings.
Date
17 July
18 July
Correct
GMT (UTC)
11h
30m
00s
11h
30m
00s
Chrono. time
11h 32m 00s
11h 32m 01s
Average daily rate (ADR) is found by using the formula:
(error on last day observed) - (error on first day observed)
ADR=
(date of last observation) - (date of first observation)
ADR formula for a 3 l-day month. A navigator desiring to determine the
chronometer rate compares the chronometer directly with the Washington,
D.C., (NSS) 1200 radio time signal on different days. On the first day the
chronometer reads fast by 9 minutes 3.0 seconds and on the last day it
reads fast by 9 minutes 53.5 seconds. ADR is found as follows:
ADR =(F) 09m 53.5s - (F) 09m 3.0s
(31) - (1)
50.5s diff =
30 days
No attempt should be made to determine chronometer error closer than
l/2 (0.5) second. Average daily rates, therefore, are somewhat a more
accurate measurement of the chronometer’s performance than are the daily
checks because, in the former method, any daily observational errors are
averaged out.
5-18
Error
02m 00s
02m 01s
Chrono.
rate
+ls
= 1.68s/gaining
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