tm has three meanings:

1. Product trademark: The TM mark does not protect the trademark. It is different from R. TM is the abbreviation of TradeMark, which includes both the registered trademark R and , also includes the direct use of unregistered trademarks that have not been approved and registered by the Trademark Office;

2. Melting temperature of DNA: DNA in its natural state will denature at relatively high temperatures (70-90°C). At this time, the double helix unwinds into single strands and becomes a random coil. This is similar to the melting phenomenon of general crystals. The temperature at which the color enhancement effect reaches half of the maximum value is usually called the melting temperature (or melting point) of DNA, represented by the symbol Tm;

3. An extremely rare unit of length: 1Tm is equal to 10^12 meters Equal to 6.7 astronomical units.