Step 13.28 — PROBE_ACCURACY at the bed centre, cold¶
Step 28 of 54 with a helper · Chapter 13 — Initial startup
(no image — see text)
Parts: none.
Do: G28, then G0 X175 Y175 Z10 F6000, then PROBE_ACCURACY.
Send: PROBE_ACCURACY
Recv: // PROBE_ACCURACY at X:175.000 Y:175.000 Z:10.000 (samples=10 retract=3.000 speed=10.0 lift_speed=10.0)
Recv: // probe: at 175.000,200.000 bed will contact at z=2.077500
... (8 more)
Recv: // probe: at 175.000,200.000 bed will contact at z=2.075000
Recv: // probe accuracy results: maximum 2.080000, minimum 2.075000, range 0.005000,
average 2.077250, median 2.077500, standard deviation 0.001803
Check
Standard deviation < 0.003 mm, and the ten values are not marching steadily one way.
Helper Reads the range and the standard deviation off the screen and writes them down.
What you're looking at
PROBE_ACCURACY probes the same spot ten times and reports how far the readings scattered. It measures the machine's repeatability rather than the bed: a tight standard deviation means the gantry returns to the same height every time.
Note: [probe] y_offset: 25.0, so the probe sits 25 mm behind the nozzle — that is why the reported probe Y is 200 when the nozzle is at 175. Older Klipper prints these lines as probe at 175.000,200.000 is z=2.077500; same thing.
Tip
values that trend are mechanical: Z pulley grub screws, Z belt tensions. Random scatter is usually probe mounting or cable. The hot test at Step 13.32 is the QGL gate.
Source: Voron startup wizard § Probe accuracy check · Klipper docs § PROBE_ACCURACY · Klipper probe.py