How to calibrate a temperature sensor
Physicist's answer ahead:

Prepare a bowl of (melting) ice water on a day where the barometer is near 1013 mbar of pressure. Stick your sensor in it. The reading you get at equilibrium is your 0C reading.

Prepare a pan of slowly boiling water, also on a day where the barometer is near 1013 mbar of pressure. Stick your sensor in it. The reading you get at equilibrium is your 100C reading.

Divide the intervening range into 100 equal parts.

The beauty of this method is that you are not tied to errors made while calibrating the sensor you are using to calibrate with, or errors made when calibrating the sensor they used to calibrate the sensor you are using to calibrate with, or ... (etc).