The Messermeister Angle Guide is a great way to train yourself in developing the ability to consistently sharpen a knife at the same angle. It approximately sharpens Chef’s knives at a 15 degree angle. The rolling pins assist in pushing the knife blade across the stone. It can be used on a flat water/oil stone or a honing/sharpening steel of any type. After practicing with the device, one will eventually develop the ability to free hand the stroke with amazing accuracy. Sharpening knives on a whetstone or water stone just got a whole lot easier!