Non-Harmonic tones (non-chord tones) occur with chords but are not chord members.
FIGURED BASS
Non-Harmonic tones are figured like chord tones. Non-Harmonic tones occurring after the initial attack of the chord are indicated with a change of numeral. When the Bass voice moves without movement in any upper voice, no additional figured bass is necessary. When one or more voices remain stable, a dash(-) is used to indicate the continuation of the same pitch. In root position triads with doubled root, only the voice that moves is figured. Figuring will be arranged from highest to lowest numeral.

FIGURE 8.1: Figuring Non-Harmonic Tones
Figuring for non-harmonic tones occurring at the initial attack of a chord (suspensions, appoggiaturas, and accented passing tones), results in figured bass which does not represent the true position of the chord. Usually, achord's position is represented with the resolution of the non-harmonic tone.

FIGURE 8.2: Figuring Non-Harmonic Tones at Initial Attack
DIATONIC PASSING TONE
A diatonic passing tone fills the interval between two chord tones a third apart and occurs in a weak rhythmic position.

FIGURE 8.3: Diatonic Passing Tone
ACCENTED PASSING TONE
Occasionally the interval of a third is filled with a non-harmonic tone which occurs in a strong rhythmic position. This is called an accented passing tone.

FIGURE 8.4: Accented Passing Tone