what type of thermometer you are using? What accuracy?
First, you can get calibration certificates for different temperature range.
What we do:
We are using thermocouples, i.e. a reading equipment with different thermo couples each having a certificate for a certain temperature range (color coded; different sensitivity classes etc).
Sensitivity: For some measurements +/- 1 °C is sufficient, for others +/- 0,1 °C is needed -> the less the sensitivity the broader the range of claibration can be.
Stability: For hot reading you need another material stability than for ambient conditions.
-> all these can be handled by using different type of thermocouples
For other application we perfer to use loogers - but the questions to be answered are the same.