It's very important to keep a sharpening angle consistent on a guided knife sharpener. The angle should not change when replacing one sharpening stones to another. In order to control the sharpening angle, one measures the angle between the knife plane and the sharpening stone.
There are many similar digital angle gauges on the market. This model is very light, which is a huge advantage when using with conjunction with a knife sharpener.
If you have a question regarding this product, please feel free to ask.