[Perfectlap]

well you're not really looking at the map/diagram while you are driving.
Actually come to think of it I don't think I have ever even looked down at my speedo while autocrossing.
The map helps if you're that type of person that remembers things a little better if they write them down first. Just like when you were in school.
While studying the map I will memorize "the directions" afterwards for instance with eyes closed I will visualize the lap:
"Left, quick right, long straight, right, six pin into hard left, slalom, right, long straight."
Downhill skiers and downhill moutain bikers do the same thing before doing their runs.
I once watched a sports car racer describe a course to a TV reporter before the race started. While the driver described the lap from memory the TV crew played the on board footage for the at home audience and the timing of both was 100% perfectly synch'd. The lap was 1:49 or whatever and the driver described the course in 1:49...Really amazing.