Woodlouse
Well-Known Member
Tradition, based upon paper charts being expensive & precious items of knowledge - no plastic coatings way back then. Hence great care taken with them, which obviously includes a soft pencil (easier to erase & doesn't cut the paper fibres).
Damage or loss, could seriously spoil your day.
Ah well. Sadly tradition doesn't play much part in sailing any more. Otherwise we'd all be doing so dressed in peaked caps and ties.