flexi-bot/docs/marlin/_gcode/M405.md

tag	title	brief	author	requires	group	codes	notes	parameters	example
m0405	Filament Width Sensor On	Enable filament width sensor flow control	thinkyhead	FILAMENT_WIDTH_SENSOR	control	M405	Requires `FILAMENT_WIDTH_SENSOR`.	tag optional description values D true Distance from measurement point to hot end. If not given, the previous value will be used. The default startup value is set by `MEASUREMENT_DELAY_CM`. unit type cm int	pre code Start measuring filament width, adjusting flow M405

Turn on the filament width sensor and start using it to do flow control. Initially, the filament between the sensor and the hot-end will be treated as the nominal width.