when measuring external static pressure with a magnehelic gauge, and you change your ESP to a CFM reading using a chart, what is the recommended CFM you should get or does it vary? im not really familiar with this? i was told your ideal ESP should be around .5 '' WC is this correct? sorry if this is a dumb question but my company does not even have one of these gauges and im pretty sure i need to get one!!!!!! any help would be great thanks!!!!