A very rare example of a vintage diving chronograph watch by Charles Nicolet Tramelan. The chunky brushed s/s case measures in at 41mm or 45mm including the oversize, screw-in winding crown and it is 48mm lug to lug. Quite a big watch, with a very rare plexi that has a Boron Tube [“Profondimètre”] on the perimeter, allowing water to enter from a tiny opening at 3h, to measure depth [please scroll down for a more in-depth explanation of how this theory works]. We have cleaned and polished the plexi, maintaining its vintage look, as a replacement is close to impossible to find. The magnificent honey brown dial and golden hands and applied indices are in fantastic condition and, combined with the golden bezel, really do steal the show. The watch is fitted with a great quality brown calf leather strap [rally style]. We have included many photos, including some fun macro shots we took. Feel free to ask us for any further information you might need.
The theory behind the “Profondimètre”: on the outer part of the crystal, there is a circular tube [known as the Boron Tube], circa 0.30 mm in diameter, filled with air. This tube has a tiny opening at 3 o´clock. As soon as the watch is submerged, the opening of this tube is blocked by the water, and the air that is still inside the tube is trapped. The deeper you go under water the more the air in the tube gets compressed, because the water moves further into the tube. The tube, when filled with air, is opaque [you cannot see through it], but when the water moves in, that specific part of the tube becomes transparent because there is metal coloured ring underneath the crystal that ‘reflects’ against the liquid. When this happens, the diving depth is indicated by how far the coloured transparent part becomes visible, which can be read on the dial scale.