I remain amazed. I gave a simple answer, which was implicitly endorsed by
another person, but which has been ignored.

"The Lady from Philadelphia" recommends the following...

Place the conventional thermometer you trust and the transmitter in the same
shaded spot. Make a chart with the transmitter's readings in the left
column, the thermometer's readings in the right column. Check the digital
thermometer's reading whenever you care to. When there's a change, walk out
of the house and read the conventional thermometer. (Such an exhausting
trek! Bring plenty of food and water, along with sunscreen and plenty of
books to read. Hire a sherpa to carry it all.) Add both values to the chart.

Is there something wrong with a simple solution? Tell me, I want to know.
Really.

We are talking about a (presumably) cheap digital/remote thermometer, which
likely has //no// calibration controls. (If it has any, it's probably just
one, for a temperature around 75F.) What is it with this hacker mentality
that demands wasting time on something that is just not that important?