Who'd have thought someone would come up with an Ipod app for pétanque!
You take a picture of the boules layout, and then center a circle with adjustable radius on the target ball. The first boule to touch the circle is closest. Very simple.
Available for $0.99 here: BoulOmetre Petanque
Of course it only works with Ipod software.
It reminds me of "Le Juge" a magnifying glass contraption with circles we sold 9 years ago. It worked quite well, but the supplier went out of business.
Thanks to Ken of Petanque Marinière for "pointing" it out!