Monochrome Watches
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Heritage Watch Manufactory Firmamentum – a complete navigational tool for the wrist

| By Frank Geelen | 6 min read |

The new timepiece from Heritage Watch Manufactory is more than just a timepiece. No tourbillon, no gongs to tell the time, no… it’s a complete navigational tool for on the wrist called Firmamentum.

Although Heritage Watch Manufactory is still a very young brand, they have already made name with their magnificent chronometers, like the award winning Tensus (that features a constant force mechanism). The new Firmamentum is by far the most complex, displaying hour angles used by navigators and astronomers to locate stars and ones own position. Lucky for us mortals it also tell ‘normal’ time.

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That ‘normal’ time is actually the solar time, that people from all around the world use to determine time. The aperture between 4 and 5 o’clock indicates “SOL” which means the watch is indicating solar time. The push button at 2 o’clock makes it possible to switch from solar time to sidereal time; the aperture will display “SID” for sidereal time.

Due to the rotation of the Earth on its own axis and the same direction of rotation around the sun, this gives the effect that within our solar system a year consists of 365 sun- and planet-rises. However outside our solar system, 366 sun- and planet-rises are measured in the same period. The system of time that splits the year into 365 days is thus called solar time, and that which splits a year into 366 days is known as the sidereal time. This results in a daily difference of approximately 4 minutes between both time systems. Accordingly, the length of one sidereal day is 23 hours, 56 minutes and 4.0905 seconds. The special Firmamentum gear train that measures the difference between solar and sidereal time is so precise that the difference per day is only 0.0005 seconds.

This is possible due to a unique mechanism with a variable-speed gear train. HWM Caliber 870 comprises of 483 parts and no less that 92 jewels! It features the Heritage patent applied for Vivax balance and Tenere fine adjustment. Like all timepieces made by Heritage WM the Vivax balance is large, 16 mm in diameter, and makes 18,000 semi oscilations per hour. All movement parts, visible or non visible, are finished and angled by hand.  Master watchmaker Karsten Fraessdorf is responsable for designing and building caliber 870.

To understand more of all dispays on the Firmamentum, it might be good to read about John Harrison on Wikipedia. He was the first to provide the theory (and working clocks with enough accuracy) of how to determine ones position on the earth. As the firmament turns, the stars and the sun in the sky appear to turn around us. This was the very basis for global positioning, before the our modern GPS made life simpler.

Every hour angle consists of a 360-degree circle. Each degree is divided into 60 units, the so-called arcminutes. These arcminutes are identified by a single quote (60′) and in their turn these are subdivided into 60 arcseconds (60″). 360 Degrees times 60′ gives 21 600′, and this result is taken to divide the circumference of the Earth at the Equator. This gives a value of 1852 metres per arc minute. A nautical sea mile is therefore 1/21,600th of the Earth’s circumference at the Equator. This sea mile is subdivided into 10 cable lengths, each of 185 metres. This means that when a ship on the Equator has travelled one sea mile, it has also travelled one arcminute (1′).

All functions can probably easily be understood by an astronomer or someone with good knowledge of navigation. However let me describe the different displays on the Firmamentum’s dial…

A = Arc hour display, 1 turn=15°, turns once an hour; can also be used as minute hand for the second time zone.

B = Short hand – Arc hour display, 1 turn in 3 hours=45°, mean solar or sidereal time
Long hand – Arc minute display, 1 turn=4′, mean solar or sidereal time

C = Short hand is the right ascension, read counter clockwise – long hand is 24hour hand for mean solar or sidereal time

D = Arc minute display, 1 turn=1°=60′, turns once in 4 minutes

E = 24-Hour and 12-hour display – long hand will turn once in 24 hours, 1 turn=360° – short hand turns in 12 hours meaning 1 turn = 180°

F = Arc second display, 1 turn=1′, turns once in 4 seconds

G = Normal seconds hand, one turn per minute

Combining hand A with the hands of display E gives the possibility to indicate a second time zone. While hand A is used as minute hand, either the 24-hour or 12-hour hand can be adjusted to indicate the hours of a second time zone.

All other displays (B, C and F) and hand D are only used for navigational or astronomical purposes.

The pusher at 4 o’clock makes it possible to synchronizes the time in accordance with a time signal. For this purpose it is equipped with a stopwatch mechanism, accurate to a second, that is activated by the pushbutton in the four o’clock position; as soon as the pushbutton is released, the watch recommences operation. Both pushbuttons are protected against accidental operation by means of a screw-down protector.

Astronomers and navigators can determine the position of stars or their own position, by calculating the angle between two planes. One plane goes through the earth’s axis (from north to south) and a meridian, the other plane goes contains the earth’s axis and a given point. Firmamentum measures the motions of the earth, sun and other planets (in or even outside or solar system) with the help of hour angles, which the watch does for both solar and sidereal time!

There are different ways of measuring one’s position on the Earth’s surface. The first, and the most natural way of observing this, is that of the azimuth. The basis for this is given by the location of the observer. He observes the horizon and, with the help of a device that measures degrees — a sextant — he determines the height of a heavenly body above the horizon as he sees it in front of him. When determining terrestrial locations, things that stand out in the landscape or buildings can be used as the starting point. This gives the first coordinate. For the North direction it is given from 0 to + 90 degrees, and from the South direction from 0 to – 90 degrees.

Eric Giroud was again responsable for the design of Heritage Watch Manufactory’s newest timepiece. This resulted in an elegant watch, that measures 44,50 mm in diameter and just 15,35 mm in height. While displaying such a variety of indications with 13 hands on the dial side, I think that’s an acomplishment on itself.

Main characteristics:

  • Hour angle instrument for the observation of heavenly bodies by means of 13 hands with two additional displays


  • Hour angle variable for either sidereal and solar time, arcdegrees, arcminutes, 5 /100 arcseconds
  • Solar time hour angle display in arcdegrees, arcminutes, 5/100 arcseconds
  • Power reserve display with balance wheel stop mechanism
  • Status display for basic regulation of Vivax balance wheel
  • Display of solar time as astronomical time
  • Second time zone settable to one minute of accuracy
  • Time in solar or sidereal time
  • Status of sidereal or solar time with variable hour angle, synchronisation mode

You can find more detailed information on the website of Heritage Watch Manufactory and keep informed about their latest news on their official Facebook page.

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