Our coach has built-in hydraulic and air leveling systems, with a display that shows the level:

We pretty much always use hydraulic leveling, as it is more stable. In theory we just use Auto mode and it works… but sometimes on a rather unlevel site we have to switch to Manual to convince it to actually be level:

A useful addition to help check how level it is is a bubble level that shows two dimensions at once:

We put it on the floor to help see how level the coach is, and guide adjustments to get it level.