Also Consider: Empire Level em95.
Not so much because ads are annoying but because the developer deserves at least that much for creating this app.
The position and visibility make it a great forward mounted set up.
Some run on higher voltages, such as 36V or 60V 54V max.
For Android, Spirit Level is a better option because it contains no ads.
In this class, we turn to Empire Level and their True Blue vials.