i made the same mistake of measuring air temp when i first got a gecko. i am surprised i didn't fry the poor thing! also, you can always make a guess by watching where they spend all their time- if they spend it all in the cold side, or in their humid hide, the tank is too warm. if they spend it all huddled on the warm side, tank is too cold. if some on each, all is well. assuming your gecko isn't too scared to come out when people are around, that can effect their thermoregulating. if you're really in doubt, get a repti-hammock, it gives them another level to chose from in terms of temperature.
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marla
currently: 0.0.9 catfish, 0.1 ferrets, 0.0.2 strawberry hermit crabs, 2.8.3 leopard geckoes, 0.0.13 oriental fire-bellied toads, and 0.2.0 sugar gliders