If we want the correct measurement result, we should not forget the following rules:

Measurements performed in stable conditions constant. This will ensure that the environment will not distort the measurement results
The temperature depends on the measuring site
During the day the temperature changes of up to 2 ° C. We can measure the lowest temperature in the 4 AM and highest at 6 PM
Temperature measurement should take place at least 30 minutes after waking or physical exertion