Granny says put the slices in a bag with a drop of oil, and shake to coat them. I didn't, I put about a teaspoon of oil on the microwave glass plate and spread it around with my fingers. Then arranged the slices, they must be thin.
Microwave for about 3 minutes, but it's best to keep your eye on them. It will steam up a bit so open the door and wipe the condensation from the inside, so you can see when they are ready. Keep checking them, don't walk away, and this is what you get, delicious crisps. The plate by the way is a breakfast plate not a dinner plate, but still quite a lot for one potato.