This set of guides helps keep a consistent angle when sharpening knives on a whetstone.

Includes a slot to attach a rubber band which wraps around the whetstone to keep everything in place.

Includes guides for edges cut at 15, 17, 20, and 25 degrees.

Unsure what angle you need?  As a general rule of thumb most eastern style kitchen knives will use a 15 or 17 degree angle, while western knives will use 20.  

If you want to confirm the angle is correct try painting the edge of the blade with a sharpie and give it a few passes on the whetstone.  If the angle is correct it should evenly remove the sharpie marks.