Hi @camilomati!
My colleague and Power User @vgon_alves has covered the topic in this post: Gauge Pressure. Tell me if that covers your question. Another post that might be of relevance here:
Please note that the pressure you set is not necessarily the atmospheric pressure! Zero inlet pressure means it is the reference pressure regardless of which absolute value it holds. If that something is still not clear feel free to ask again.
Best,
Jousef