Those are pretty accurate, as long as you are measuring very close to the surface area. (the gun itself should be very close before you press the button).
Check the batteries as well, if they are getting old, that may throw measurements off.
As dragons do move about during the day, he may be using the basking spot but you just don't see him in it often. What is the temp of your basking area by the way? It should fall within 95-115F with the higher end for younger dragons. Also, is the basking spot easily accessible for your dragon? (not to steep, or slippery so he can't climb up). A narrow basking area may not be very appealing to your dragon, maybe try a wider log/brick. I find dragons like wider basking areas, where they can sprawl over, exposing more of their body to the light.
Dragons with good basking setups will bask as soon as they wake up, in the hottest area they can reach (as high as 120F, if available) for awhile and then move off into cooler areas. Also, after eating, they go right back into that hot basking area for while, then will move to cooler basking areas.
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PHLdyPayne