flexi-bot/docs/marlin/_gcode/M915.md

tag	title	brief	author	deprecated	requires	group	codes	notes	parameters	videos	example
m0915	TMC Z axis calibration	Align ends of the Z axis and test torque	thinkyhead	2.0.0	TMC2130,TMC_Z_CALIBRATION	control	M915	This command is deprecated. Use `G34` ([`Z_STEPPER_AUTO_ALIGN`](/docs/gcode/G034-zsaa.html) or [`MECHANICAL_GANTRY_CALIBRATION`](/docs/gcode/G034-mgc.html)) instead. Requires `TMC_Z_CALIBRATION` and at least one TMC driver for Z axis. If `Z_DUAL_STEPPER_DRIVERS` is used, both should be TMC drivers.	tag optional description values S true Current value to use for the raise move. (Default: `CALIBRATION_CURRENT`) unit type mA int tag optional description values Z true Extra distance past `Z_MAX_POS` to move the Z axis. (Default: `CALIBRATION_EXTRA_HEIGHT`) unit type linear float	JqH41K2vq0g	pre code Set a 300mA current and press the gantry against the top for 5 extra mm. G21 ; Units to mm M915 S300 Z5

The command aims to align the ends of the X gantry (for a Průša i3-style printer). See the video demonstration above.

Using the given current, Marlin will move the Z axis (at homing speed) to the top plus a given extra distance. Since this intentionally stalls the Z steppers, you should use the minimum current required to move the axis.

Z is then re-homed to correct the position.