The following screen captures are from a screen-video-capture of an RTH that I did from around 400m-500m during a basically windless 'window'
I may try this in a not "windless 'window'" to see what "speed", as used in the manual, means.
1) = sticks centred, D=477m, return journey just starting, speed 1.3m/s , recording time t=2.48
2) = sticks centred, D=437m, steady state, speed around 8m/s, recording time t=2.55
3) = sticks centred, D=295m, steady state, speed around 8m/s, recording time t=3.13
4) = R stick fully forward, D=211m, peak speed 14.3 m/s, recording time t=3.21
5) = R stick easing off, D=89m, manual slow down speed 13.5 m/s, recording time t=3.29
The drone was in Sport mode through out this procedure.
Between the start of the RTH and screen capture 3 I left the sticks alone.
Just after screen capture 3 I pushed the right stick fully forward (controller stick mode = 2). Screen capture 4 was approximatley the fastest flight speed.
Shortly there after I began to let the right stick centre for a gradual slow down rather than a "slam on the anchors" stop, screen capture 5 shows this.
When the feeling takes me I will repeat this with the drone in P mode and then C mode.
With regards to the graphical plot. It shows, for a series of these RTH's, the output plots from CsvView for
a) in light green, distance from the home point (m)
b) in red, speed (m/s)
c) in purple, the right stick input
d) in light green, the "pitch" of the drone (presumably in degrees)