I realize this may be a stupid question, but I've been switching blades every 5-7 shaves just because somewhere I heard that I should. But the thing is, I have a really light beard. Mostly peach fuzz except right under my chin. (Damn that Dutch/German/English/Native American heritage! ) So I was thinking, isn't there a good chance that I can get away with using a blade longer than a lot of guys? So how do I know when it's getting too dull? Presumably I don't want to keep pushing it until it just won't cut hairs anymore.