Zenith Chrono Cal. 143-6 Tropical

This Zenith Reference 143-6 is a military pilot chronograph from the 1950s with a tropical dial.

Zenith reportedly received an order from the Yugoslavian military in 1954 to develop a chronograph for their pilots. The new military watch should be of high precision, reliable, robust und easy to read. As a result, Zenith produced this two-register chronograph that was powered by the reliable manual wind movement Excelsior Park 143-6. Yugoslavian Air Force ordered about 2000 pieces and handed them over to their pilots.

The dial of this vintage watch was originally black. In the long lifespan of over 65 years, this chronograph was repeatedly exposed to light and sun. Little by little the dial color changed to a beautiful brown hue that you see today. Such dials are called tropical by vintage collectors. The white hands provide a nice contrast. The dial bears only the Zenith star and the Zenith word at 12 o'clock. The sub dial with the small second is at 9 o'clock. The chronograph's minute counter at 3 o'clock covers 45 minutes, with the first 10 minutes being highlighted with longer markers.

Another rare feature of the dial is the original radium luminescent material. Before 1963 it was still allowed to use the material radium for the luminous hour markers and hands. When radium was classified as highly radioactive and dangerous for watchmakers in 1963, watch companies had to switch to tritium. We were able to detect the original radium lume of this particular Zenith with a Geiger counter (see pictures). This proves the originality of the dial, but also that the luminous material has never been repainted.

The Zenith Chrono has a round stainless steel case with a diameter of 37mm. Thanks to the thin bezel, this Zenith does not look too small on the wrist and is very comfortable to wear. For a watch that is over 65 years old, the condition is absolutely impressive. The case back still bears deep engravings including the watch's serial number. The lugs still have their original beveled profile.

The movement of this watch is Excelsior Park caliber 143-6. Zenith used the movements of Excelsior Park until 1960 and Martel movements from 1960. The caliber 143-6 is very robust and still keeps time very accurately. The chronograph starts, stops and resets perfectly.

Serial number: 9105xxx

Int.Exe.: 50310