Yes, because often (usually) a blade is V shaped from heel to tip, so if you line up the back of the blade horizontally, that means that the sharpened edge of the blade angles down in the clamp. The rules of geometry tell us that when the blade angles down, the sharpening bevel angle (using a fixed pivot point) changes. So it is better to have the sharpened edge horizontal and the back of the blade on an angle in the clamp. so using fine markings on each side of a vertical ruler, you can get the blade closer to horizontal, and therefore, the bevel angle will be more consistent, right?
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