The WeightAide app for iPhone and Apple Watch provides a simple way to review and update your Apple Health weight information from either your Apple Watch or your iPhone.

The apps can run independently on each device type, so for example, full update, history and graph functionality is provided on the Apple Watch, which can be operated without the need to install the WeightAide app on your iPhone.

There are benefits to installing the app on your iPhone as this will allow the Watch app to request the full set of weight data from Apple Health instead of being restricted to the last 7 days of data, which is the default for all Watch apps.