Welcome to the forum, Steve. The degree markings are per side so match the number, do not divide in half. Be aware the angle indicators are just an approximation. They will get you close to 20 degrees. Realize that same 20 degree setting will give varied results depending on the size of the knife and the clamping position. If it is important to you that 20 degree setting is accurate then a digital angle cube should be used as a tool to help you adjust the WE more precisely.
The ceramic stones are used as is. No water, no oil. They do have a break-time, as do all the WE stones. That means the abrasive action will improve over time with more use. It’ll become more uniform, consistent and predictable.
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