I am looking for a thing! It is a type of ruler. Are any of you looking for a thing that you can describe but cannot find? That as soon as you know the word for it you'll be off like a light but until then you are sitting in frustration staring at incorrect search results? Currently looking for: Spoiler: Drawing ruler that rotates at 0 does there exist a ruler that rotates at 0cm/"/whatever? googles just giving me instructions for rotating rulers in like clipstudipo and photoshop I want to be able to alight the 0 on a physical piece of metal/wood/plastic to a dot on my paper and then move the other side of the ruler to my destination and look back at the 0 and it's still on the dot whereas right now I align the dot and move the other side and look back at the 0 and put it back at the dot and then adjust the end of the ruler back to the destination and repeat until they actually alight until I slip and move the ruler and I am frustration perhaps a ruler with a channel down the center? you put a pencil at 0 and rotate around that?
Best guess is maybe a carpenter's folding ruler might do something similar to what you need, or possibly a sliding bevel gauge?
Hmmm... a bullseye ruler is almost right, if instead of a big rectangle cutout and a slide it had a much thinner cutout just big enough for a pencil tip. The red circle seems to be able to be pushed down in a way that keeps the bullseye centered on point A, but with the size of the cutout finding the center to put it on point be is more difficult, though I suppose one could just slide the slide at the same time as rotating. Reviews indicate they might be cheaply made though.