Showing distance along the route

Hello

I'm wondering if it is possible to alter the distance between markers along a route?

I've created a 300 odd mile route and whatever zoom level I'm at in the map the distance markers seem to be 10 miles apart. My recollection from previously is that this can be altered to say 5 miles or whatever you want. I can't find any setting for this however so maybe I'm just imagining the facility?!  Thank you for any help.