How do F1 drivers park in their grid slots?

Might sound a silly question but I have always wondered this. F1 drivers cannot see the ground in front of their cars so parking exactly in their grid slot would be tricky id imaging. How do they ensure they are not ahead of the slot risking a penalty or behind it a bit so as to disadvantage themselves?|||it is not the white dot ahead of the grid box... it's the extended yellow line (runs parallel to the wheel axis to the either left or right) that serves as a guide...





EDIT: actually that yellow line is only to the right side of the driver... sorry...|||check next time u will se a small white dot bout the size of a coin 3 ft in front of each gridline, its a guide but they so used to it i doubt the f1 drivers really use it|||they know how far out the nose of the car goes or at least have a very good idea and know how wide it is so they can be in very accuratly, and ive seen some cars go slightly ahead of the line but they do not get penalized|||If they can stop their cars in the pitbox to a centimetre accuracy, parking in their grid slot should be a piece of cake.|||its all accuracy :)|||i guess they must be able to see something and well they do have world class instuition aswell