A tipping tip

Ever wonder how much of a tip you're supposed to leave? Here is an article "20% is the new 15%" that spells it out for a variety of different services. I always tip at least 18% at restaurants and when I get my hair cut. Normally I shoot for 20, and sometimes even more, depending on rounding, circumstances, and different things. I've never had much need to know how to tip most of the other occupations listed.