# Z04 Automatic Zero Offset
### Definition
This function recalibrates the flow meter zero point (0 flow) by resetting the output to zero.\
For ultra-low flow measurements, zero calibration helps correct zero-offset errors and improves accuracy.
The function starts after pressing **Start** and automatically updates **A22 (Auto Zero Offset)** upon completion.
**Recommendation**\
It is strongly recommended to execute **Z04** when measuring flow rates below **10% of full scale**, as small zero offsets can cause significant errors at low flow.
**Example**
* Zero offset: **0.2 L/min**
* Actual flow **100 L/min** → error ≈ **0.2%**
* Actual flow **0.5 L/min** → error ≈ **40%**
{% hint style="info" %}
Parameter Z is not supported for Modbus read/write operations in the current version.
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### Notes
1. Perform Z04 when the pipeline is **fully filled with liquid and the liquid is completely stationary**. Performing Z04 when the pipe is not full may cause flow measurement errors and unstable readings; if this occurs, repeat Z04 under full-pipe conditions.
2. **Repeat this procedure after every reinstallation or when changing pipe size or material.**
3. The **Z04** function is equivalent to **A22**; users can choose either.\
(Z-series parameters are designed for quick setup, consolidating multiple essential settings to streamline installation.)
### Operation Procedure
Button Functions (Click to Expand)
The main unit has **four buttons**. The **bottom line (Line 3)** of the LCD displays the current function of each button. Under normal operation, the button functions are as follows:
* **Blue Button -** Leftmost button: Return, exit, or save settings.
Gray Arrow Buttons:
* **Left Gray Button:** Page up, increase value, or select item
* **Right Gray Button:** Page down, decrease value, or select item
* **Orange Button:** Rightmost button: Enter settings, edit, or confirm selection
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**Do not hold buttons for extended periods to avoid damage.**
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{% hint style="info" %}
Button functions may change depending on the operation context to improve usability or prevent accidental presses.
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{% code fullWidth="false" %}
```
Z04 Automatic Zero Offset Setting Steps
• From the main screen (green backlight),
press Orange Button (Setup) to enter settings (orange backlight).
• Use Gray Arrow Buttons to select Z. Easy Setup , press Orange Button (Enter).
• Use Gray Arrow Buttons to start Automatic Zero Offset
• Device shows “Start auto Z04” when automatic zero-flow begins.
• After ~30 seconds, it displays “Set zero offset to ____”.
• Then it returns to Z04 Auto Zero Offset, indicating completion.
```
{% endcode %}
