Definition

A line may request 150 mm/s but be too short to accelerate to that speed and decelerate safely. At corners, the planner also limits the velocity change so the mechanism does not attempt an impossible instant turn. These limits strongly affect time, vibration and surface ringing.

The word 'jerk' is dialect-sensitive. Marlin classic jerk describes an allowed instantaneous speed change, while Klipper uses square_corner_velocity within a different look-ahead model. The numbers are not equivalent settings and should not be copied across firmware.

What matters in practice

Short moves stay slower

Dense curves and small infill segments may never reach their programmed feed rate.

Corners share speed

Look-ahead joins adjacent moves and chooses a safe junction velocity.

Terms differ

Marlin jerk, junction deviation and Klipper square-corner velocity are related ideas, not interchangeable values.

Example in G-code

Two motion states

M204 P800 T1500
M205 X8 Y8
G1 X100 F9000

Marlin-style commands set preferred acceleration and classic-jerk limits before the move; actual results remain bounded by firmware and hardware.

What this viewer can show

In this viewer

The viewer uses supported M204/M205 state and a bounded planner model for a more realistic duration than distance divided by F. It remains an estimate, not firmware-identical simulation.

Primary sources

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