Well, rulers  rule. That is just about it. We have different rulers, for to make different types of lines and circles too. People tend to underestimate the usefulness of a rule when drawing. Most of my lines and curves are real straight. Still, it is good for drawing sceneries and the like.  The rules are from different brands and whatever. Not all rulers are made the same way. This is more for people who draw in the real world. In computers, the lines can be done with the program. I hope you find it useful. Rulers wise, Bazic is always a good option. Staedtler also has some decent rulers. They are good both for drafting and for school purposes. We like to cater to all artists, both novices and experts. That is how we roll. I hope you find this selection useful.