MIL-PRF-46374G
3.5.8 Dark viewing. After being subjected to the readability in total darkness environment of
table I, and without any intervention on the part of the observer, the luminous features of the
watch shall be of sufficient brightness so as to be readable in total darkness while holding the
watch no closer than 30.5 cm (12 inches) from the eyes of a dark-adapted observer having normal
or corrected 20/20 vision.
3.5.9 Isochronism. Watches shall pass the test for isochronism specified in 4.6.5.16, in a dial-up
position at 23.9 °C ± 1 °C (75 °F ± 3 °F).
3.5.9.1 Type I class 4. The watch shall be fully wound and operated for 4 hours. The watch
shall again be fully wound. The rate shall be recorded while fully wound and then at the end of
the 4th, 20th and 24th hours. The difference in uniformity of rates between 4-hour periods shall
not exceed 10 seconds.
3.5.9.2 Types II and III class 4. The variation in rate shall be recorded every 6 hours for a period
of 24 hours and shall not exceed 5 seconds from the rate recorded in the previous 6 hour period.
The watches shall be fully wound prior to testing and shall not be wound during the test.
3.5.10 Accuracy. After being subjected to all of the environments of table I, the mean daily rates
of the watch in each of the two positions of (1) dial-up and (2) crown-down shall not exceed the
values at the temperatures specified in table III.
TABLE III. Accuracy.
Type I,
Types II and III, Types I, II and III,
Class 4
Class 4
Classes 1, 2, and 3
Temperature
Mean daily rate
Mean daily rate
Mean daily rate
(Seconds per day)
(Seconds per day) (Seconds per day)
4.4 °C ± 1.1 °C (40 °F ± 2 °F)
±120
±60
±3
23.9 °C ± 1.1 °C (75 °F ± 2 °F)
±60
±30
±0.7
51.7 °C ± 1.1 °C (125 °F ± 2 °F)
±120
±60
±3
3.5.11 Long term accuracy (Qualification only). Accuracy shall be determined during a 90 day
period as specified in 4.6.5.24. During the 90 day period of operation, watches shall be subjected
to vibration and shock after 30 days and 60 days of operation in accordance with 3.5.1 and 3.5.2,
except that duration of vibration shall be for only 5 minutes in each direction. Watches shall meet
the criteria of table IV.
3.5.12 Altitude. Types II and III watches shall show no evidence of damage or adverse effect on
operation when subjected to the altitude environment of table I.
3.5.13 Salt fog. Types II and III watches shall show no evidence of damage to the crystal, the
case, or the watch band or adverse effect upon operation after having been subjected to salt
atmosphere in accordance with the salt fog environment of table I.
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