Have you checked the specs on your instruments? Most cheap digital ones are +/- 2ºF or worse some are +/-4ºF and +/- 10% humidity.
My cheap analogue one is +/- 2% Humidity and I don't use my analogue thermometer with my snakes but it is specd at +/- 0.5ºF. Yes you can get that accuracy in digital but it costs. I have never found a digital hygrometer/thermometer that was as accurate for anything close to the 35$ I spent on them.