Dividers are a great tool for precise measuring because of their very fine endpoints. They firmly hold an exact distance, and can easily be adjusted.
A scribe is good for etching marks on the metal. I use a scribe when drawing a line to be cut or when placing a dot for drilling. Removing scribed lines requires a lot of sanding: first with a coarse sandpaper and progressing through higher grit (smoother) sizes.
|Carbide scribe & adjustable dividers|
Rulers with millimeter notations are also helpful.
|Useful hash marks|
Pencil and sharpie are good alternatives to a scribe when lines and markings are required for visual aid. They last long enough in my experience to finish a task, yet remove easily from the metal with only a light sanding.
Intersecting pencil lines allow me to determine where to drill.