How far could the legions travel in a day

[Caius Fabius]

I served in the (foot) Infantry, and was involved in the sport of Orienteering.
We usually counted our own paces, and in the infantry, while moving across country, at least one person was the "pace man" per squad. Then at a rest, we could compare the paces, and see how far we had traveled.
The Romans had a cart invention that measured the distance traveled by the turning of a cart wheel and the dropping of stones, if I read the books correctly, but I doubt that you need to have this when you have soldiers who can count. Why would you need a slave? Counting the pace is a great way to keep your thoughts away from your blisters.