The Stryd platform offers the ability to merge watch data from Polar and Suunto with data stored on Stryd (by doing an offline sync). This allows Suunto/Polar users to get all the advanced metrics in one data set, even though the watches do not record LSS, VOSC and other advanced data.
Here is a break down on the source of each metric you see in PowerCenter:
Please note: The merge algorithm favors watch data for pace and distance. Hence, if the watch recorded distance is different than Stryd distance (because the watch was set up to use GPS for pace/distance or the watch applies a calibration factor to the Stryd data), the watch distance/pace will be stored whereas the Stryd pace/distance information will be ignored.