Hold on a minute!

Stocktaking time at the zoos.  Easy enough to count the elephants - not so simple when it comes to fish and insects.  Which reminded me of an article I once read entitled "How to measure a fish" - the point being that it's pretty well impossible to accurately measure anything which is moving.  In order to accurately measure anything you need to be able to fix the position of both ends at the same instant in time, and of course with a moving object by the time you've established exactly where one end is, the other end will have moved. Which, by the way, is the basis of Einstein's relativity concept that a moving object will always be measured as shortened in the direction it is travelling.  Of course, you can always cheat by taking a photograph and measuring the image.