This one's probably a bit OCD
At the airport on arrival I count how many people are queuing to get through passport control.
Divide it by 3 (based on my estimate of average group size)
Then count how many staff are manning the desks.
Then time how long it takes on average for a group of 3 to get through.
Then do the maths in my head to estimate exactly what time we will get through.
And every five mins I go through the same process and adjust the prediction accordingly.
Sad I know.
Never get anywhere close. I'm always way too optimistic on how quick it will be.
Took us about 75mins to get through at sandford. And messed up our meal booking in universal.