Why the temperature of the mat surface is so low and changes so much?

If you keep your mat open without a protector pad on it, the heat is radiated and dissipates in the air. As soon as you lie down on your amethyst mat or cover it, the temperature becomes more stable. 

It is very important that you cover the mat completely while preheating it.

If you cover the mat partially, the temperature sensors positioned in the different layers of the mat around all the surfaces will report different and controversial measurements to the main controller.

Finally, the controller may lose calibration and start to work incorrectly or malfunction.

So, please, always cover the mat completely while it is preheating to set level.

When pre-heated, the crystals radiate heat very quickly. Cover it with a pillow and measure the temperature beneath in 10 minutes, and you will be surprised by the difference.