Why is pencil used to draw a line on paper in chromatogram?

Pencil is used to draw a line on paper in a chromatogram because pencil marks are made with graphite, which is insoluble in the solvents typically used during chromatography. This ensures that the line remains stable and does not interfere with the separation of the substances being analyzed. Additionally, pencil lines provide a clear reference point for measuring the distance traveled by the compounds.