Maintaining a vegetable garden gives plenty of opportunities for such quick predictions, even for sequentially updated ones. 'I have to weed the carrot rows. But I have only done them last week! Surely there will be less than a hundred weed seedlings?' -> 'Oh, this is how it looks today! Okay, raising the estimate to 150.' -> 'My back! Why do I grow carrots, anyway? It's a carpet of weeds!':)