Quarter-tone flat (reversed flat)

In Stein–Zimmermann 24-EDO notation, the reversed-flat sign lowers the written pitch by one quarter-tone, half a semitone. Similar-looking signs can mean different adjustments elsewhere, so a contemporary score's legend takes priority.

Family: Accidentals
Where it sits: Just before the note
What it looks like: A curve or arc, A straight line

Do not confuse it with

A normal flat lowers a semitone; this reversed flat lowers half as much only within the stated system.

What the sources say

SMuFL — Stein–Zimmermann accidentals (24-EDO) W3C Music Notation Community Group
accidentalQuarterToneFlatStein — Reversed flat (quarter-tone flat) (Stein)
Unicode request for Stein–Zimmermann quarter-tone accidentals Unicode Consortium
The Stein-Zimmermann quarter-tone flat sign ... is a reversed flat
MusicXML accidental-value W3C / MusicXML 4.0
quarter-flat quarter-sharp three-quarters-flat three-quarters-sharp

All notation signs