1. Enter your user profile details correctly. When you compare the readings from iOS to android or vice versa sometimes entered height is not exactly the same. hence it may vary the results.  

2. Check whether you had enabled the athlete mode which you had never been used before. 

3. Make sure you are measuring with empty stomach.  

4. While comparing results also consider the water retention level. (body water %)

5. Do not try to measure your body compositions with Dry footprints. moisten your footprints little bit before measure body   compositions. 

6. Take your measurements at the same time each day to ensure the most accurate results.