First of all, please know that the measurement of different brands of the scale (or the scale at the gym/hospital) is based on their own algorithm/formula, so it is normal if you see different readings from different sales due to the difference in their algorithm/formula.

As for Eufy Smart Scale, the body fat % and other body compositions are calculated from the user's bioelectrical impedance, his/her profile (gender, age and height), and our own formula. Please understand the Eufy Smart Scale is a simple home appliance for you to measure and it cannot be taken as a precision medical measurement machine. It is recommended to track your body's weight info via the data trends.
 

Here are some tips. 

1. Reinstall batteries, and turn the scale on, wait until " 0.0" is displayed before measuring to calibrate.

2. Make sure the scale is on a hard and flat surface.

3. Wipe your feet with a damp cloth, keeping them slightly damp.

4. Check to make sure your personal information like age, height, gender are complete and correct. (This scale is calibrated to more accurately measure the body composition of users between 16-80 years old. )

For the P2 series, you can also refer to the video below to troubleshoot:
eufy Smart Scale P2 Series: How to Troubleshoot Inaccurate Body Measurements
 

If you still have some concerns about the data of your body fat%, please email eufy support with a screenshot of your profile (shows the gender, height, and age) and the health details for further check whether the result is correct according to our formula.