horiba TW-150 Instruction Manual page 76

4 CALIBRATION
The screen shows that the calibration is complete.
9. Press [YES].
The turbidity zero calibration coefficient is updated.
10. Close the valve of the calibration tank.
11. Disconnect the calibration tank from the calibration inlet of the device.
Span calibration <turbidity>

Follow the instructions given in "  Span calibration <turbidity>" (page 45).
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