I have a free app on my tablet (but not on my phone) that turns the tablet into a level for leveling my Interstate. I entered the length and width of the wheelbase and saved the info. Then by setting the tablet flat on the floor or the galley counter, it will directly read out exactly how high each low corner of the van has to be blocked to get it level with the high corner. The only drawback to the app is that all dimensions are in millimeters, and I have to mentally convert to inches because that's the system I grew up with.
I don't have my tablet handy to get the name of the app that I use, but you should be able to search the app store for "RV Leveler" and find several similar offerings. And there should be similar apps for leveling trailers, too, but since I don't have a trailer I never looked for one.
I thought getting old would take longer!