What does Swiss T 25 mean on a Rolex?

Swiss T <25 is a marking that you may find on a Rolex Explorer II Ref. 16570. This marking signifies that the watch is Swiss-made and contains a certain amount of tritium that emits less than 25 mCi (millicuries). Tritium is a radioactive isotope of hydrogen that is commonly used in the luminescent material of watch dials to make them glow in the dark. The use of tritium in watch dials was prevalent in the past, particularly during the 1960s-1990s when it was the material of choice for luminescence. However, due to its radioactive nature, tritium has been phased out in favor of safer alternatives such as Super-LumiNova or tritium gas tubes.

The "<25" in the marking indicates the specific level of tritium radioactivity in the watch. In this case, the watch emits less than 25 mCi of radiation. This designation is important for collectors and enthusiasts who are concerned about the potential health risks associated with radioactive materials. It's worth noting that the use of tritium in watch dials has been regulated over the years. In the past, higher levels of tritium were commonly used, but as safety concerns grew, regulations were put in place to restrict the amount of tritium emissions. This is why you may also come across vintage Rolex watches with the marking "T Swiss Made T," which indicates that the watch contains tritium that emits less than 7.5 mCi. If you happen to own a watch with the Swiss T <25 marking, it's important to understand that the level of tritium emission is considered safe for regular wear. The radiation emitted by tritium in such watches is minimal and poses no significant health risks. However, it is always advisable to exercise caution when handling any radioactive materials and to consult with a professional if you have any concerns. The Swiss T <25 marking on a Rolex watch indicates that it is Swiss-made and contains a controlled amount of tritium that emits less than 25 mCi. This marking is a testament to the watch's quality and craftsmanship, as well as its adherence to safety regulations regarding tritium use.