I think most people are using their phones to set incline. To be honest- when i first started I too checked. Now I play the game and set it where I want it. I DONT CARE what the level says- and it dont matter. You cannot break a game by setting it too steep or shallow- although I suppose since ball speed goes up a bit if its steeper you could theoretically see an effect from that.

Just keep it such that the levelers have enough thread sticking out the top to keep it secure. Thats about it!!

Those bubbles in the plastic tube and holder are cheap and not always accurate.

I use an inclinometer .

These might help :

http://www.pinballnews.com/learn/iphone2/index.html

http://www.pinballnews.com/learn/iphone/index.html

http://www.pinballnews.com/learn/level/index.html

LTG : )

Normally you set it up so the top of the bubble is somewhere between the bottom two lines. That gets you between 6 1/2 and 7 degrees. That's a start. Now play the game and adjust it up or down to your taste.