The results of the measurements taken with BIA (How does TANITA measure body composition?) devices are always calculations and estimates based on the (measured and entered) data available about the body and the validated equations.
All our devices are perfectly suited to detect and display changes in the body when comparing a series of consistent measurements taken weekly over a longer period of time. We use different technologies and evolutions of the BIA technology for our different devices. Therefore, when using different Tanita devices, differences in the results can be expected (for some people even big differences). Part of the differences are due to normal day-to-day fluctuations (which you will always see), but part is due to the differences in technology. Some examples of the different technologies are segmental and non-segmental scales, dual frequency and single frequency, 4C technology, etc. In general, we recommend not to compare measurement data obtained with different devices.
In order to get a good picture of your body composition and any changes therein, we recommend that you create a series of consistent measurements, with the same scale, that you can compare to each other. Read here: How to get the best results from my TANITA?