Unlike a knife, a razor's proper edge angle is built into the geometry of the blade itself. The razor's blade becomes it's own sharpening angle guide. When a razor is laid flat on a hone, the edge angle is set by the thickness of the spine and the width of the blade. That's why a flat hone can be used to sharpen any width razor. A razor's blade geometry is really rather an ingenious solution to enable lifelong sharpening with a flat hone yet maintain a relatively constant and sharp edge angle as the years pass. A razor's blade is a well thought out tool that uses a simple principle that endures, turning a grooming task into an enjoyable hobby.