I have been browsing the video options through the RGUI the other night, and I found the Estimated Monitor Refresh Rate entry. Letting it run for 2048 frames, then pressing OK on it sets the value for the sync.
I am wondering if it is necessary to go to the RGUI at every new PC or monitor that RetroArch is ran.
If I have RetroArch on a pen drive and plug it here and there, then launch it straight into the wanted ROM, does Dynamic Rate Control take care of the sync procedure even if RGUI had not been visited before?