In a single room, it is common to see a difference in temperatures between two different devices if they are not located close to each other.
The temperature and humidity displayed in the Home + Control app are measured by the Netatmo Smart AC Controller. To make it as accurate as possible, do not prevent air from circulating around the product and do not cover it (curtain, radiator shelf, casing, etc.).
Your air conditioner is also fitted with sensors that tell it when to switch on and off depending on the orders received from the Home + Control app.
Those sensors are not synchronised with the Home + Control app so a discrepancy can occur. In this case, your AC's sensor will remain in control and signal to your AC when it should turn ON or OFF using its readings.
Temperature calibration is not available in the Home + Control app.