As a Master HVAC tech, I can tell you that the *IDEAL* situation is 75F @ 50%RH. This will give you ideal conditions and will keep you from having any mold issues with the plants and buds. there is a very narrow bell curve where molds and viruses will *NOT* grow. With the ideal being 75F @ 50%RH, you can only go 5% either way. Use the most accurate measuring instruments you can afford, then find a psycometric chart and plot your temp and RH.

My grow temps range from 78 - 80F with RH at 45 - 50%. It plots out on the the chart to the equivelant of 75 @ 50%.

If you want healthy, this is the way to go.

FWIW, a good instrument to start with is digital sling psychrometer/thermo hygrometer. Its a combination meter that does Relative Humidity, Dry Bulb temp, Wet Bulb temp, and dew point, and reads in either F or C. They are around a hundred bucks, and are accurate enough for me to do my job with.