two diff temp readings on heat mat

so i have a hydrofarm thermostat plugged my heat mat into it set the probe in the enclosure dead center on the heat mat and its reading at 86.9(still heating up) and my acurite is reading 3 degrees about it..and they are both right next to each other under the substrate

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Originally Posted by volkert13b

so i have a hydrofarm thermostat plugged my heat mat into it set the probe in the enclosure dead center on the heat mat and its reading at 86.9(still heating up) and my acurite is reading 3 degrees about it..and they are both right next to each other under the substrate

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Assuming both the probe and the accurite are correct, it is not uncommon to have a few degree variance across the face of a heating element.

I would check temps with a heat gun and determine if that is the case, or if it's a case of one device being more accurate than the other.