Carrie, with this first hatch, I think it's best to do it the way Deniece is. Fill your C trough like the directions say. Put your AcuRite unit outside the bator on it's little stand, thread the probe's wire anywhere through the edge of the bator and into the water wiggler, placing the wiggler across the egg racks, perpendicular not parallel, so it won't get stuck and the racks will just turn underneath it easily. Then go by the probe reading in the wiggler. It doesn't have to stay exactly on 99.5. Mine cycles between 99.2 and 99.9 and all of those are just fine. If you can find a smaller thing to measure humidity use that (do NOT use the white square Springfield with temp/humidity because it's awful) or just do as the bator instructions say and fill the appropriate trough.
Your AcuRite readings are on all the time unless they've put an on/off switch on that unit. You can tell at a glance what the temp in the wiggler is.