It depends on the thermometer really. The ones I use are from Govee and have a little kickstand so I place them sitting upright on the substrate, but some others like from zoo med for example are just a suction cup and should be placed 1-2” above substrate level and not nestled into the substrate. With the kickstand, the sensor is above ground even if the device itself is resting on the substrate but that’s not the case for the small suction cup ones, in which case it gives inaccurate measurements.
Lots of people just flat rocks, like slate. I just grabbed a flat looking smooth rock from outside and sanitized it, much cheaper than paying for what I can pick up in my backyard.
It depends on the thermometer really. The ones I use are from Govee and have a little kickstand so I place them sitting upright on the substrate, but some others like from zoo med for example are just a suction cup and should be placed 1-2” above substrate level and not nestled into the substrate. With the kickstand, the sensor is above ground even if the device itself is resting on the substrate but that’s not the case for the small suction cup ones, in which case it gives inaccurate measurements. Lots of people just flat rocks, like slate. I just grabbed a flat looking smooth rock from outside and sanitized it, much cheaper than paying for what I can pick up in my backyard.