The iHealth AM3 tracker records all your activity (physical activity, exercise and sleep) from 0h to 24h. It resets to zero at midnight each day (number of steps, distance covered, calories burned, level of activity). Unsynchronised data will not be lost, but will be stored in memory until the next synchronisation*.
To save time, daily synchronisation is recommended. Your iHealth AM3 can record up to 14 days of data.
Note - Be careful, synchronisation of 14 days of data when your smartphone is connected in 3G/4G can consume a lot of data.
*If you have not synchronised your iHealth AM3 for more than 14 days, the oldest data in memory will be overwritten and replaced by newer data.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/205766612-iHealth-AM3-When-should-I-synchronise-