Suspend carries manufacturer setup charts for the common Fox, RockShox, Öhlins, Marzocchi, Manitou, and Cane Creek forks and shocks, so those get a charted air pressure and sag range straight away. Pick yours when you set up the bike. If your exact unit is not charted, Suspend still works: it starts you from a weight-based estimate, tells you it is an estimate, and tunes from your sag and your ride feedback the same way.