Decidedly not!
There are minimum and maximum speeds with radar guns all along the course. Some people get REALLY competitive.
Some people use high precision GPS that gives them an average speed to 0.00X mph. Others use GPS that gets them to the tenth of a mph.
We use visible references with notes showing time to be there and stopwatches.

My first attempt at navigating got us a 0.745 second time error.
My first drive got us a 0.147 second time error.
My second drive got us a 0.0.020 second time error.

We were nearly a full second off on this drive down. Luckily, we were able to make it up on the way back.