Apple’s new support document says that the new Apple Watch Series 8 may need five days to set a baseline wrist temperature.

The document covers the Apple Watch Ultra and Series 8 models, and iterates that the user will have to have the smartwatch attached to their wrists in order to detect their base temperature.

As it stands, there are two sensors for the newer Apple Watch models- one at the back crystal and another under the display. While the user is resting, the sensor takes readings every 5 seconds for up to 5 nights. This is done to reduce bias, according to the Cupertino-based company.

During this time, Apple recommends enabling the ‘Track Sleep with Apple Watch’ feature, as well as Sleep Focus for at least 4-5 nights. After the process is over the user can check their recorded measurements in ‘Body Measurements’, then ‘Wrist Temperature’ in the Health app.