Do you have observations downloaded that are in the area of the grib file?

It works by comparing the downloaded weather station observations with the grib files rather than your own boats data.
On the weather panel there is a button for downloading the observations.

Thank you for your answers.

With downloading observation, it's work.
I understand it's a snapshot at the current time. But as I have a significant number of observation and plenty grib array values, where is the difference calculated? At nearest observation of the boat?

The difference of pressure is not calculated?

I have downloaded the observation of the different stations ok UK and France, + the one of the boats in the channel. So several observation stations
In the results, I have one line for Arome model and a second one for UKV. For witch station is it ?

At this point, it only uses the most recent.

It uses all ASCAT data loaded though.