Blue is calibrated at the factory, so a calibration is not necessary when you receive it.
For the following years, the probe must be calibrated at the beginning of the season.
Depending on the environment of your pool, other calibrations may be necessary.
If you have any doubt about the calibration, do a test via the app. Place Blue in pH4 and take a measurement in Bluetooth. If the pH value is more than 0.1, please follow the calibration procedure in the app in "Settings"> "My Blue Connect"> "Calibrate Blue Connect".
More information here to know how calibrate Blue.