The movie starts with John Garrity (Gerard Butler) as an engineer on a construction site looking over some designs and taking some notes with a Pentel GraphGear 500 mechanical pencil. It is a disaster movie, a comet is going to hit earth and, and a few selected people are notified to go to a shelter.
This is the first and last time the pencil appears in the movie, but I am sure the pencil survived the comet and is still working today.
In the rest of the movie, you can see the trip to the shelter and all the misfortunes that happen on the way.I do not know if the crew chose with a reason the Graphgear 500 over its bigger brother 1000 (braking issues) or it was just what they had lying around. Either way I think this is a solid choice, in case of a disaster, to have such a good mechanical pencil.