Spirit Levels, Pocket Levels
The further development is the digital spirit level, which can indicate the desired angles even more precisely - i.e. in the range of millimetres.
To cut a long story short: you always need a spirit level! Aligning washing machines, hanging shelves, aligning cupboards, etc.
What length should your spirit level have?
Basically, the spirit level should be at least half the length of the object to be aligned. The longer the spirit level, the more accurate your measurement. In plain language: a small pocket spirit level will have a deviation of approx. 1mm at 1m. If you use a 30 cm spirit level for the same work, the possible deviation is only 0.5 millimetres per metre. The 30 cm model is therefore twice as accurate!