NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.7

Using Arduino Sensors
210

Interesting discussion Tim. I disagree about timestamps. Here's how to synchronize 2 Uno's to 2us.
As you can see they stay in sync even without GPS once initialized.
http://arduino.cc/forum/index.php/topic,120288.0.html