In figured bass, accidentals that are not in the key signature must be specified:

• The alteration symbol is written before or after the number corresponding to the note in question.
• If the alteration symbol appears by itself, it applies to the third above the bass
• A slash through a number can be used to raise a note by half a step

Here are some examples:

An example from Bach's cantata Ach, lieben Christen, seid getrost (BWV 114). We show the chord notes in the upper staff without pretending to make a musically correct realization of the bass. Note the use of the slash to indicate an F sharp in the first bar:

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