Empty octaves are mostly played with the thumb on one side. That´s why we don´t write it´s number but write the possible fingers 3 or 4 or 5 in the normal five-finger-position-way (see also example 10):

Filled octaves have always finger 1 and 5 at the edges, if they have three voices you write only the middle voice, if they have four voices it is only necessary to write if you take finger 3 or 4 because you always need 2. Lines over and under a number show that the number relates to the middle of a chord (see also example 14).

In special cases you can relate a line of chords also on a five-finger-position with exceptions:

At the often-used octave-arpeggio in the same sense the octave grip is marked not with 1 and 5 but easier visible with the so-called octave-bracket which contains the necessary middle-numbers 2 or 3 or 4.

At arpeggio over more than one Oktave you can make a little sharp edge at the beginning of the bracket to indicate over-size: