Definition

Filament, Bowden tubes and molten plastic behave elastically. When motion accelerates, some early extruder movement builds pressure instead of immediately increasing flow; during deceleration, stored pressure can keep pushing material. Firmware compensation changes extruder motion around those speed changes to reduce bulging and under-filled line starts.

The concept has different names and commands. Marlin uses Linear Advance and M900 K, Klipper exposes SET_PRESSURE_ADVANCE, and RepRapFirmware uses M572. Their numeric factors are based on different implementations and units, so values must be calibrated within the target firmware and hardware setup.

What matters in practice

Not retraction

Retraction primarily relieves pressure around travel; pressure advance acts continuously around print-speed changes.

Calibration-specific

Extruder path, nozzle, material and motion settings can all change the useful value.

Firmware-level effect

The compensation can alter stepper motion without changing the XY path written by the slicer.

Example in G-code

Three different interfaces

; Marlin
M900 K0.18

; Klipper
SET_PRESSURE_ADVANCE ADVANCE=0.04

; RepRapFirmware
M572 D0 S0.1

The values are examples only and must not be converted or copied as equivalent settings.

What this viewer can show

In this viewer

The viewer shows the commanded toolpath, not the firmware's stepper-level compensation. It does not simulate or validate pressure-advance tuning, and the command page labels that limitation explicitly.

Primary sources

This explanation uses firmware documentation and details visible in G-code. Your printer's settings still determine what the machine does.