One of the digital thermometers ranges from about 66-86.

Does it have patches that change colour to indicate temperature? If so,
that's an LCD thermometer, not an electronic digital thermometer, and
unlikely to be very accurate.

Sorry I was thinking of a glass tube thermometer, that is, an analog device.

The trouble with digital is the rounding error. On analog you might read 70
and a half.
But one digital might sense it as 70.45 and report 70 and another might
sense 70.55 and report 71.

More likely, the digital thermometers will display fractional degrees.
So the one will report 70.5 and the other will report 70.6. It probably
won't be *accurate* to 1/10 degree, but have enough precision that you
don't have to worry about roundoff error.

This is exactly why I bought a glass thermometer just to check my digital
thermostat. They are less than $5.

Analog glass thermometers have infinite measurement precision (you can
use a magnifier to resolve fractions of one scale marking), but their
accuracy is not infinite, and depends on manufacturing accuracy. There
are accurate and inaccurate digitals, accurate and inaccurate analog
thermometers.

Dave