The most impressive timepieces from the Heritage series of Longines Watches are two models that are modern recreations of the iconic timekeeper made especially for the first man to ever fly over the Atlantic Ocean, Charles Lindbergh. They are equipped with the tools that were conceived by the famous pilot in order to enable the navigation during long and challenging flights. Though supplied with the identical functions, these models with the same name include different self-winding mechanical calibres. This is caused by the different proportions of the timekeepers. While one of them replicates the size of the original Lindgergh’s timepiece (constructed in 1931), the other one is made in the smaller scale and is less exclusive. This can be seen in the fact that it has a mineral crystal, while the bigger model has a sapphire instead.
The most prominent trait of the watch is its hour angle feature, enabled with a rotating bezel, a rotating central dial and three scales that correspond to the three hands of the watch. This feature allows the wearer to determine the current position, or to be more precise, the current longitude. For many of those who do not know what hour angle is, here is the explanation. As the Earth makes a complete rotation (of 360 degrees) in the period of 24 hours, one hour represents the hour angle of 15 degrees. Similarly, if an hour angle measures up to 15 degrees, it means that the current location has a time zone that is one hour off the GMT (Greenwich time).
Complex Procedure of the True Pilot’s Instrument
The Lindbergh wristwatch includes the mentioned principles in its functioning. For this reason, hour hand moves 15 degrees during one hour (indicated by the blue Roman numerals that show a 180 degree rotation during twelve hours), while the minute hand moves through a single degree every four minutes, which is likewise equal to 15 degrees per hour. On the bezel of the watch, we can see an engraved scale that divides a single degree into four sections of 15 minutes. Besides, the second hand makes a full revolution, which is equal to 15 minutes (of a degree), and for this reason, the rotation central part of the dial, besides the scale of 60 minutes (of an hour), is also divided to 15 minutes (of a degree).
In order to be able to determine the exact location, it is necessary to use some of the other instruments as well, and the most important of those are sextant and the Astronomic almanac that includes a table of orbital placements and the rotational orientation of the celestial bodies.
Longitude Calculation with the Use of the Difference of the Hour Angles
The starting point of successful navigation is the calculation of the latitude. This can be performed with the use of sextant that measures the height of the North Star, and then utilizes a scale to convert this measure into the present latitude. This leads to the process of calculating longitude by figuring out the difference between the hour angle of the Greenwich meridian and the one on the current location.
The next step in the process of determining the hour angle of the Greenwich is adjusting the reference mark on the bezel of the Longines watch that bears Charles Lindbergh’s name. The bezel should be rotated in order to take account for the equation of time, and this is done with the help of the information from the Astronomical almanac. Furthermore, it is necessary to set the watch to GMT time, which is executed with a turn of the crown to the right position. When this is done, the wearer can calculate the hour angle by adding the number of degrees on the scales shown by hour, minute and second hands. Subsequently, the wearer should return the bezel to the neutral position, and then calculate the solar time (solar time represents the hour angle of the Sun, and can be calculated by a sextant and the almanac, or with a sundial) at the location. This can be done with the use of sextant, an almanac and latitude (or with a sundial) and then the wearer should set the watch to that time. The final step in the complex procedure is to figure out the difference between two hour angles, and voila, you got your current longitude. It is also very important to note that the timepiece also utilizes radio time signals to adjust the seconds hand to the correct position.
As it has been mentioned, there are two modern incarnations of the Lindbergh’s watch. The first one with the reference number L2.6184.108.40.206 is larger, and has the same diameter of 47.5 mm, just like the original timepiece made for the famous pilot by Longines. The case is made of stainless steel, while its back is stamped and can be opened to unveil the view to the functioning of the movement. This transparent back is like the front side made of sapphire crystal.
Inside the case beats the mechanical automatic L699 caliber with 24 jewels, the frequency of 28,800 vph and a power reserve of 46 hours. The outer dial of the pilot’s watch is white and lacquered polished, completed with blued Breguet-style hands made of steel, whereas the inner segment is in silvered opaline shade. The final touch is a brown alligator leather strap.
The smaller of two Lindberg’s watches has the same type and shape of the case, but with the smaller diameter of 38 mm. Also, the dial is the same as in the larger version. Its beating heart is L614 self-winding mechanical calibre with the same frequency as the previous one, four jewels less, and a power reserve of 42 hours. The wristlet used in this model is made from black genuine leather. Both models are water proof to 30 meters.