The tempurature you are most concerned of is the temp under his warm and cool side hides. If you do not have a helix or device that controls the temp for you I would highly suggest purchasing one.
The helix will control your heat mat and lamp so the temp reading from its probe is always at your desired range. With the helix I place the probe under the hide on top the substrate since I am most concerned with belly heat temp...not the temp and inch or so above the substrate.
If you cannot afford a helix or temp control device I would still use the temp probe and place it on the substrate under the warm hide. This belly heat temp of the substrate is your benchmark for your warmside temp. You can do the same with the coolside temp probe...Lay on the substrate in an area the snake may be less likely to disturb but do not have it under something since it will not get the radiating heat from above. I am new to the ball world but these are just my thoughts...Best of Luck
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