Whatever you do, DON'T believe those people who insist that you must slice the peel first, and then boil it.
Boil the fruit first, and slice it when it's soft and forgiving. Then put the sliced peel, pulp, and a muslin bag containing the pips (extra pectin for setting, and a bit more bitter flavour) back into the liquid and use a pound (450-ish grams) of sugar to a pint of liquid.