What, exactly, makes a pen a "user grade" pen? I see this term all the time, and am sure it applies to most of my pens...is there a specified amount of wear on an older pen that puts it in this category? Or something unusual like a really deep scratch or a personalization or a cap that doesn't quite fit? I'm asking for knowledge, but I'm also asking because, if I decide to sell any of my pens, I want to be able to describe them properly. Thanks.