Hi flythisway, I was taught to use permanent Lumocolour over head projector pens the very fine ones, (the water soluble ones will smudge and smear if, like me, you get hot and sweaty in exams). Your pen lines will come off the glossy surface of the chart quite readily if you use a decent eraser like the the Staedtler mars plastic.
As for calculators not sure about the legality of using one, but from memory I only used the wizz wheel. Don't forget it is not just the track and heading but also the ground speed and leg timing.
All the best with the exam.
Chris