From their website:
Set of 1 dial.
The Mecha Heat Dials are perfect for tracking the heat buildup during the game. Each dial is marked from 0-29 with the 30 spot (SD) or Shut Down. Now you can easily track the heat level of your mecha right on the table top.
These dials require assembly. The magnets should be press fit into the center hole cutouts, be sure that the polarity of the magnets match then snap the dial halves together for the finished dial.
Note: the dial photographed has been enhanced by coloring in the etched numbers with a white crayon, see the instructional image to see how to achieve this look for your self.