Moving walkway: Slider control - for what?

[qcs2017]

There's a slider control on the moving walkway. It's not labeled and it does *apparently* not do anything. Is this just a small bug or does this slider something useful? I could think of something like movement speed as result of that slider... Any hints?

[chick10000]

movement speed. it does move PAX faster,

[qcs2017]

As I said, I thought it could be movement speed, but I didn't see anything.
Now I checked with a second moving walkway next to the first, and set the sliders to the extreme left and right. Now I really see a difference. Very subtle. Maybe +/- 5% from the center setting? It feels like the difference between bare concrete and floor tiles, that's why I think it is 5%. I was hoping for at least 25% at the highest speed compared to standard walking speed? Real Life airport moving walkways seem to do between 2x and 4x the normal walking speed, from what I found quickly skimming the net.