[justforasingle]

I bought a copy of TASCHEN's "The Elements of Euclid" with illustrations by Oliver Byrne from his book in 1847. As I was working through a lot of the later problems I could see myself causing these sorts of errors due to a skill issue. For example as I dragged the pencil vertically down a ruler the wooden side of the pencil (above the lead) rested on the ruler. As I dragged the pencil down my arm lowered and my wrist changed orientation so that the lead of the pencil was now resting against the ruler as I completed the line. It was honestly so frustrating to see the corners and arcs of my diagram look like abstract dog shit because I was too much of a dumbass to use a ruler correctly.

[mbivert]

For that kind of things, lead-holders are preferable: you at least get a consistent lead width, despite the wearing, assuming you maintain the orientation of the pencil.

An alternative is to sharpen your pencils with a utility knife & sandpaper: it's more versatile and less wasteful than a regular sharpener. For example, you could sharpen it to an edge (like a slotted screwdriver), and turn the pencil once in a while, so that the wearing helps preserving the edge.

I've also dabbled with Islamic patterns recently. Side-note: I've found some high-quality, cheap second-hand compass sets, that used to be used for wood work a few decades ago (not made-in-China).

[gilleain]

Yes, I've learned some techniques after reproducing a lot of Islamic patterns, which can be done entirely with straightedge and compass (although frankly I often 'cheat' by using measures, grid paper and tracing paper, lol).

Indeed the movement of the pencil can matter a lot, as can how good your compasses are. I've found that a bevelled ruler can be better if turned over so that the pencil rests against the bevel. Otherwise you have to take account of the width of the pencil lead and adjust the ruler position to take account of it.

Certainly small errors in line position, length and (especially) angle can have a huge effect over a large diagram that has a lot of symmetries. It's surprising how noticeable even a small error of 0.5 mm between two lines is that should be colinear.