Tare and calibrate

Before the station can weigh anything, the scale needs two things: a zero point for the empty platform (tare) and one known weight to learn from (calibration). You do both once after building the station, and again only when something changes.

Before you start

The load cell and platform are mounted and the platform moves freely. See Scale platform and enclosure.
You have an object whose weight you know exactly, in grams. Anything from 1 g up to the load cell's capacity is accepted; a weight close to a full spool (around 1000 g) is a practical choice. Weigh it on a kitchen scale if you are not sure.
The platform is empty: no spool, no reference weight.
The station has been switched on for about 15 minutes. The board and the load cell warm up after power-on, and the reading drifts while they do. A calibration made right after switching on can read a few grams low or high later.

Choose the load-cell size

The station supports two sizes of the YZC-133 load cell: 5 kg (the default) and 2 kg. If you built with the 5 kg cell, skip this section.

Browser: Settings → Scale → Edit Load-cell profile.
Set YZC-133 variant to 5 kg or 2 kg. The line below shows "Rated capacity: 5000 g" or 2000 g.
Click Validate and save.

Warning

Changing the load-cell size deletes the calibration. Calibrate again afterwards.

There is no load-cell choice on the touchscreen.

Overload threshold ratio in the same form sets when the station reports an overload: 1.10 by default, which is 5500 g on the 5 kg cell and 2200 g on the 2 kg cell. Allowed: 1.01 to 2. It is a warning only and does not protect the load cell from too much weight.

Calibrate on the touchscreen

Tap Settings, then Calibrate scale. On a station that has never been calibrated, the first button on Home reads CALIBRATE and opens the same panel. During first-run setup it is CALIBRATE NOW.
With the platform empty, watch the yellow guidance line: "1. Waiting for stable empty platform" becomes "2. Ready to tare".
Tap TARE EMPTY PLATFORM. The line then reads "3. Tare complete - place reference weight". If the tare fails, the line starts with "Tare failed:" and gives the reason, for example "The platform is not empty (reads X g). Remove everything, then tare. If it is empty, tare again within 15 seconds."; it stays until your next tap. If the platform really is empty (the zero itself has moved), tap TARE EMPTY PLATFORM again within 15 seconds.
Put the reference weight on the middle of the platform. The line may read "4. Waiting for stable reference weight".
Check the number in the field under "CALIBRATION". It starts at the weight you used last time, or 1000. Tap the field to change it ("Calibration weight") and enter your reference weight in grams.
When the reading is steady, tap RUN CALIBRATION (the line may read "5. Ready to calibrate"). The button can be tapped only once the reading is steady and the number is valid. If the line reads "Enter the known reference mass", the number is missing or larger than the load cell's capacity.
Wait a few seconds. When the calibration has worked, the panel closes by itself and the first button on Home reads WEIGH. If it fails, the panel stays open and the line reads "Calibration failed:" followed by the reason, until your next tap.

RUN CALIBRATION can be tapped only after the tare, with a steady reading and a valid reference weight. Close leaves the panel without calibrating.

Calibrate in the browser

On the Dashboard click Weigh, then open Scale setup in the dialog. Settings → Scale → Recalibrate scale opens the same dialog with the calibration panel open.
With the platform empty, wait for "Ready to tare." Click Tare and confirm "Tare the scale now? The platform must be empty and stable." You see "Tare complete."
Click Calibrate. The panel "Calibrate scale" opens with a checklist: Empty platform, Tare, Place reference, Stable signal, Calibrate.
Put the reference weight on the platform and type its weight into Known reference weight (g).
When the status reads "Reference is stable. Ready to calibrate.", click the Calibrate button at the bottom of the panel and confirm "Calibrate using N g and the saved load-cell profile?".
You see "Calibration complete."

The status line walks you through it: "Waiting for stable empty platform.", "Ready to tare.", "Tare complete — place the reference weight.", "Waiting for stable reference weight.", "Reference is stable. Enter its known mass.", "Reference is stable. Ready to calibrate."

Check the result under Settings → Scale: the Hardware card shows Scale as "Calibrated".

Check the result

Leave the reference weight on the platform and weigh it like a spool (touchscreen WEIGH, browser Weigh). The gross weight should match the weight you entered.
Take it off, put it back and weigh again. The result should repeat.

If the results do not repeat, look at the mechanics before calibrating again. Weighing a real spool is described in Weigh a spool and save the weight.

Tare on its own

Tare sets the reading of the empty platform to zero. It is not the weight of the empty reel; that comes from Spoolman (see Where the empty-spool weight comes from).

Touchscreen: Settings → Calibrate scale → TARE EMPTY PLATFORM, then Close. There is no tare button on the normal Weigh page.
Browser: Dashboard Weigh → Scale setup → Tare.

Tare only with an empty platform. The station refuses a tare while the reading is still moving. Once the scale is calibrated, it also refuses a tare while the platform reads more than 50 g: "The platform is not empty (reads X g). Remove everything, then tare. If it is empty, tare again within 15 seconds." (On the touchscreen this follows "Tare failed:".) Remove the spool and anything else, then tare again. Before the first calibration the station cannot tell the weight, so make sure the platform is empty yourself. Each tare, including the one at the start of a calibration, first re-runs the scale converter's own offset calibration, so the new zero matches the converter's current temperature. You do not need to tare before every weigh: when the empty platform has drifted a little, the station corrects the zero by itself.

When to do it again

Situation	What to do
You changed the load-cell size	Calibrate. The old calibration was deleted.
After a factory reset or a USB install	Calibrate. Both erase the calibration, and a settings backup does not contain it.
You rebuilt the platform, moved the load cell or changed its wiring	Tare and calibrate.
A weigh fails with the empty platform reading below zero. The browser says "Scale zero has shifted. Empty the platform, then use Tare in Settings > Calibrate scale and retry."; the touchscreen says "Measurement failed or timed out. No inventory update".	Tare. Calibration is not needed.
A known weight no longer reads correctly	Tare first. If it is still off, calibrate.

A firmware update over Wi-Fi keeps the calibration.

Tips for stable readings

The station accepts a weight only when it is steady: the reading must stay within 2 g for 1.5 seconds. It waits up to 20 seconds for that.

Put the station on a solid surface. Do not lean on the table while weighing.
Let the whole spool rest on the platform. Keep the loose filament end and all cables off it.
Put the spool in the middle of the platform.
Wait for STABLE (touchscreen) or "✓ Stable" (browser) before you lift the spool.
Stay below the load cell's capacity. Above the overload threshold the weigh fails: the browser answers "Scale overload detected. Remove weight and retry." and the touchscreen shows "Measurement failed or timed out. No inventory update".

If something goes wrong

What you see	What it means	What to do
Home button reads CALIBRATE, or the Weigh page shows `SETUP REQUIRED`	The scale has no calibration.	Calibrate as described above.
The line stays on "1. Waiting for stable empty platform"	The empty platform's reading keeps moving.	Check that nothing touches the platform and that the station stands firmly.
"Scale hardware unavailable" / "Scale hardware is unavailable."	The station gets no readings from the scale electronics.	Check the wiring: Wiring.
"Enter the known reference mass" or "Enter a reference weight within the selected load-cell capacity."	The reference weight is empty, zero or above the capacity.	Enter the weight in grams, up to the capacity.
"No reference weight detected. Place the reference weight on the platform and retry."	The reading did not change after the tare.	Put the reference weight on the platform, then calibrate.
After RUN CALIBRATION the panel stays open with "Calibration failed: …" (touchscreen), or a pop-up gives the reason (browser)	The scale refused the calibration.	Tare the empty platform again, place the weight, wait for a steady reading and retry.
"The platform is not empty (reads X g). Remove everything, then tare. If it is empty, tare again within 15 seconds."	Something is on the platform, or the zero has moved.	Remove it, then tare. If the platform is empty, tare again within 15 seconds.
"The scale is busy. Try TARE again in a moment." or "The scale is busy. Try calibrating again in a moment."	Another scale action was still running.	Wait a moment and tap again.
"The scale stopped responding. Reconnecting to it; weighing is unavailable until it answers again."	The scale electronics stopped answering, for example after a short power drop.	Wait. The station reconnects by itself and keeps the calibration. If the message stays, check the wiring.

More: Weight looks wrong. For the exact timings and limits see Scale behaviour.