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01-30-2019, 01:17 PM
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#2
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Enlisted Member 
Drives: M5s & 06 E91 325xiA
Join Date: Jan 2019
Location: CO
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Quote:
Originally Posted by NorthernDancer
Bought 1 in Germany in the early 70's-unfortunately got stolen few years ago. My question is this: at the bottom it was "written" T SWISS MADE T. Someone once told me it stood for true swiss made time. Anyone have any further insight? Looking at high end watches today. I never see it. Simply SWISS MADE.
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Quote:
What does the "T" designation at the bottom of the dial mean?
This refers to the chemical used on the hands and hour markers, which causes them to illuminate. Around 1950, watchmakers started using Tritium as their luminous material, and began indicating the amount of that radioactive material with a designation at the bottom of the dial (i.e. T SWISS T or SWISS T < 25). Around 1998, watchmakers changed the designation to read SWISS or SWISS MADE, when they replaced the Tritium with LumiNova (an organic, non-radioactive chemical), as their source of luminescence.
T SWISS MADE T indicates that the radioactive material Tritium is present on the wristwatch. The amount of radioactive material emitted is limited to a maximum of 25 milliCurie.
SWISS T < 25 more specifically indicates that the wristwatch emits an amount of Tritium that is less than the 25 milliCurie limit.
SWISS T 25 indicates that the wristwatch emits the maximum allowable amount of Tritium (i.e. a full 25 milliCurie).
SWISS (or) SWISS MADE on wristwatches produced after (around) 1998, indicates the presence of LumiNova as the luminous material. (Please Note: "SWISS" or "SWISS MADE" was also the indication on wristwatches produced prior to the 1950s, when Radium was used as the luminous material. However, at that time "SWISS" or "SWISS MADE" simply indicated that the watch was, in fact, made in Switzerland
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Source, post 3
https://www.rolexforums.com/showthread.php?t=426209
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