Hmmmm........ I believe the level is no longer a level, but a predetermined protractor...... and a long one at that.
I wouldn't consider that a level as being used and described, either. However, it is a nice trick. My only question is....... ya know how much play is in any one of those bubbles. Will a digital always be dead-balls on regardless of what angle you set it ?? Once ya go off on angles and whatnot, the discretion might get weird. When going to the other side, do you start all over again or just flip it ?? According to what's in the truck, it might alter if you don't start all over again for the same reasons as stated on using a conventional level.