Since its creation, the clock has been closely linked to humanity’s greatest adventure, and conquering the sky is no exception. From the first test flight, watchmakers have developed practical tools to meet the needs of pilots. They are still shaping and telling the image of the awesome aviation adventurer.

Lin Bai Zheng Kong Ji

   It is worth remembering that from the 1920s to the 1940s, pilots-even aircraft engineers-were using sextant and Nautical Almanac to calculate their longitude and latitude positions, just like the crew at sea. The nautical calendar can be used to determine the true solar time of a particular date. To this day, it is still an important dependency for adventurers who do not rely on GPS navigation, but we often forget. It is also worth noting that there is a difference between the Mean Time displayed on the watch dial and the true solar time provided by the sun. This difference changes over time and is called the ‘time equation.’ The specific difference between different dates can be read from the table on the nautical calendar or advanced watches equipped with the ‘time equation’ complication (Panerai, Vacheron Constantin, Audemars Piguet, Breguet, etc.).

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   Once the true noon is determined (when the sun reaches its apex, the normal solar time is added and subtracted), and then the solar declination of the date is determined, the operator can use the sextant to perform angle measurement and calculate the latitude. It needs to be emphasized that in order to minimize the risk of calculation errors, multiple measurements are useful, because the movement of an aircraft or a ship may cause reading errors, and this risk can be eliminated by averaging calculations.

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Example of Latitude Calculation
   Let us assume that at the moment of the northern half of the hemisphere (spring or autumn equinox), the observer is located between the North Pole and the Equator. When the sun moves along an orbit from east to west and appears at exactly south (that is, the highest point of a given latitude in the northern hemisphere), if the height of the sun (relative to the horizon) measured with a sextant is 35 °, then observe The latitude of the person should be a reciprocal angle with the height of the sun, that is, 55 ° north latitude.

   After the latitude is estimated, the operator must measure the longitude again to determine the coordinate position by comprehensive latitude and longitude. In order to calculate the local hour or longitude (originating from spherical trigonometry, a special manual is now available), observers must compare the solar time at their location with a reference time, which is usually based on the Greenwich Meridian (UTC or Coordinated World) Time). In this way, the hour and angle information is obtained, and then converted into degrees, minutes, and seconds, which can be used by the navigator to obtain his own longitude position.

Principle of Longitude Calculation
   The principle of longitude calculation is very simple: the time difference between the reference time (Greenwich) and the measurement time (local) corresponds to 15 ° per hour, 1 ° every 4 minutes, and 450 meters per second. In this way, time corresponds to an angle of 15 ‘every 60 seconds (1 ° is equal to 60’ and 15 ‘is equal to 0.25 °).

Operating Longines Angle Watch
   First, wearers of hour-angle watches should be aware that in order to be useful and efficient, the watch needs to be set to GMT, just like a marine astronomical clock. The radio hour signal transmitted by the long wave helps the watch display time to perfectly synchronize with GMT.
   Although the hour-angle watch (sweep seconds) does not have a stop or reset function, Longines watchmakers are equipped with a two-way rotating inner dial (based on the Weems patent), allowing the operator to precisely adjust the sweep seconds scale, Does not affect the normal operation of the watch.
   At every hour of the hour, the radio will beep. At the last moment of the announcement, the second hand must be aligned with the inner dial ’60/15’. Mechanical watches are very sensitive to vibrations, and watches without anti-magnetic protection may change in accuracy. Therefore, it is necessary to periodically reset the time to ensure the most accurate measurement.

Determination of longitude
   After the correct Greenwich Mean Time is displayed on the dial, the observer must use the sextant to measure the noon of the sun where he is. Taking the right measurements to accurately determine longitude information is crucial to knowing when the Sun in Greenwich will reach its zenith (including jet lag), and these can be found in the nautical calendar.
   What a wearer of an hour watch needs to do is estimate the time it takes for the sun to rise to its apex. At the right time, he needs to take a series of measurements with a sextant and then compare this time to the GMT time shown on his watch. The difference between the two times can be converted into local and Greenwich longitude differences (degrees, minutes, seconds). Then by integrating previously known latitude information, the observer’s immediate position can be obtained.

Reading the hour
   If you want to use the Longines Time Angle Watch to measure the position of the observer, you must convert the time information (measurement time) displayed on the dial into angle information (degrees, minutes, seconds). The degree information (15, 30 … 180) marked below the Roman numerals can be read by the hour hand.
   In addition, in order to further refine and refine, you need to read the digital information carved on the bezel with the minute hand (1 to 15, corresponding to 1 ° every 4 minutes, and 1 ° is subdivided into 15 ′, 30 ′, and 45 ′). Finally, the ‘second’ (‘) information in the angle is completed by the second hand and the inner dial scale .