Since everyone uses leads with varying amounts of pressure and the need for depth in architectural plans and renderings resulted in the needs for many different types of leads. B Leads are darker and as you get to 9B they become more and more charcoal like. When starting to draft, always use an H, generally 4H to 9H. They are lighter in shade, with a harder lead that erases the easiest. Just be careful not to write/draw too hard, it will indent the paper resulting in issues with paper texture and eraser. You can also get a ghosting affect when shading.