The drone speed during the acquisition is calculated and set depending on your flight parameters (overlap, flight height).
The speed the drone will fly is displayed when tapping START before going to the takeoff checklist.
For the P4P, the minimum speed corresponding to Slow is 2 m/s and the maximum corresponding to Fast is 15 m/s.
Then the 3 intervals in between are evenly split between 2m/s and 15 m/s meaning that the speeds will be as follow:
2 - 5.2 - 8.5 - 11.8 - 15 (m/s)
6.6 - 17.2 - 27.9 - 38.5 - 49.2 (ft/s)
As an example, if the drone speed calculation of your flight is 25ft/s, setting up the speed sliders in the middle (27.9 ft/s) will have no impact. However, if you set it to the second interval after slow (17.2 m/s) then your drone will actually fly at 17.2 ft/s instead of 25 ft/s.
Note that those speed intervals calculations depend on the drone and it will not always be the same. Also, we recommend setting the speed sliders to Fast except for few cases where the pictures sharpness is not satisfying because of the drone speed, for example when flying at low altitude.