## Thursday, April 11, 2013

### Things I learned at Heathrow today

1. If you take a perfectly ordinary cheese,  tomato and ham baguette and put it into one of those hot, squashing panini-making machines, it cooks to something delicious.

2. If afterwards,  you use the vacant basin in the baby-change booth to floss your teeth, you will be chased away by a member of cleaning staff despite protesting "Excuse me, do you see any babies here? "

As we were driving past Stonehenge, there were the usual 625 tourists forming a strung-out circle around the stones. 'A fine example of a Poisson distribution,' I thought to myself. 'The probability of any particular tourist being here today is minusculely small .. but there are a lot of tourists.'

If we take the mean number of stonehenge tourists (625 say) as the Poisson parameter λ, this will also be the variance.  The standard deviation is therefore 25 (square root of λ). Most always the number of walkers will be within 3 std dev of the mean (i.e. 550 - 700) which explains why Stonehenge, tourist-wise, always looks the same.

Adrian arrived safely and is currently adjusting to the local time zone.