That changed when Apple added it as an option in the iPhone 4. (Previous iPhones lacked the oomph to crunch relevant data quickly enough to be practical.) Other examples include cameras and apps that stitch together panoramas from overlapping images shot in an arc around a single point or as a moving sequence.

ECONOMIST: Monitor

Older children who have outgrown the running-in-circles phase can plot an outing to an historic statue (choose from Joan of Arc or Winston Churchill, among others) or a home state street.

BBC: Visiting Washington DC with kids

Suzuki showed a patient structural command, giving an arc-like shape to the Kyrie by waiting a hundred or so bars before applying a substantial crescendo.

NEWYORKER: The Book of Bach