I use a craftsman digital torpedo level with the help of a friend. I used to be able to crawl under the game and lift it up with my back while turning the levelers.

I also have used my back for years. Starting to get harder as I get older. I heard about someone putting two nuts on their legs feet and using them with a wrench to adjust them without having to lift the game. This is the route I'm headed as games get moved in my house.

The concept is you put the two nuts against each other which locks them in place. You use the lower nut to tighten raise the foot and the upper one to lower the foot (keeps them locked together).

As far as level. I don't trust those phone apps. I have a digital level from Home Depot that I use. It has a digital readout but also the bubbles to make sure it's still calibrated correctly. Cost something like $30. When leveling I do 4 things.
First - I level the rear of the PF with the level as far back as possible and still be on the PF itself.
Second - I level the front of the PF as far forward as I can get the level on the PF itself (between the slings normally)
Third - I make sure that the changes to the front didn't effect the rear (at can be a dance sometimes)
Last - I take a ball and roll it from as high as possible to the drain and visually check to make sure it goes straight down.

I use one of these. Nice and compact so you can check level and slope all over.
https://www.amazon.com/Calculated-Industries-7434-AccuMASTER-Inclinometer/dp/B0148M7P4O/ref=sr_1_7

I have one very similar to this. Can definitely recommend... with a caveat: Like it or not, your playfield will show signs of bowing - especially if it's an older pin. You'll get one reading at the bottom, then might read 1*+ different at the top.

I gave up and just surrendered to using the bubble, but still use this level to check side-to-side both at top and bottom of the playfield.

Side note: I did a Pepsi Challenge between my level and the PinGuy app on my iPhone XR. They were nearly identical, differing by only 0.1* at the most.

Me too. Works great

I use the PinGuy app on my phone. I have checked it against a $400 digital level and it is 100% as accurate on my iPhone.

That was me. You use 2 nuts and a washer between. The washer helps keep your socket in good position. You need to jam the two nuts together fairly tight to allow you to rotate your socket in a counter-clockwise rotation and not have the jam action come undone. This way you only adjust with the top nut. You can do it the other way but with a good jam, you don't have to do any acrobatics.

Works better with a manual ratchet instead of trying to use your drill or impact driver.

Hold your level on the bottom of the cabinet. If the bottom of the cabinet is level the game is set up as intended.

How does that work if the bottom in your cabinet is sagging?

I also use the pinguy app on a apple phone, it is a bit different with a android, but works the same. The speach is good on the app.
This way you hear how to adjust and do not have to go up and down allways to adjust the legs.

Another thing:
I use coinmechs and when i try to level it to 6.5° angle, the coin goes into the reject slot.
I have adjusted the playfield to 5.5° and it plays also still fine, but the coinmechs are not allways taking the coins correctly (at least somewhat better then at 6.5°).
I know, it is because they "lean" against the coindoor, but does someone has a solution to maybe straighten them up a bit somehow.

My 2c.

Pinguy is much better i.m.h.o.

Please share the link

Its a app for Android. It is also availlable for iPhone
https://play.google.com/store/apps/details?id=com.nottud.pinballleveller

https://apps.apple.com/de/app/pinguy/id782973821