Pencils & Pens
A good pencil is an essential part of a geometrician’s tool set. Ideally, we need a least two, one for the compass and one to draw lines with the ruler. The good news is that pencils are relatively cheep and widely available.
Think about this:
Whenever you draw a line with a pencil on a piece of paper you are actually applying a very thin layer of metallic elements to the page.