What the horizontal dotted line on the Temperature diagram stands for?

In the upper part of the screen, you will have a diagram showing your body temperature reported minute by minute. On the left side, it shows the range of body temperature from 35.6 to 38.00, while on the bottom, there are shown the hours of the days (every 6 hours).

The horizontal dotted line you see in the middle of the diagram indicates the normal average human body temperature, which is 37° C (98.6° F).

Can my body temperature be affected by external factors?