Get one with a probe on it. It will give you a temp and humidity reading for the probe and an air temp. The one many of us uses is by accurite and costs about $12. Flukers has a reptile therm/hydro for about $25. A few of us have those too.
I got frustrated with the water heater regulator (tried 3 of them) and finally went to the reptile section of the pet store and bought a thermostat made for reptiles.
It keeps the ambient temp at 99.3-100.1 and the wiggler temp has been dead on at 99.5 for 7 days. It slipped to 99.7 once.
ok well I moved around the thermostat and it might have helped a bit but im still working on it I put in a rack and left it alone for the night The temp now in the WW is 100.3 will that be good ?
You might also try making the fan blow across your water source for the humidity. The temp and the humidity are closely related. That last half degree is a killer to adjust out!
But it actually should be good because the temps will change once you put eggs in and you might have to adjust it after 12 hours or a day.
so the temps are doin ok I ordered the Brinsea Spot-Check Digital Thermometer and got a 10$ one at the pet store I think i might almost be ready to put some eggs in