Maintaining momentum is the key to pacing and fast swimming - mistakes off the walls, not breathing efficiently, or an asymmetrical kick may be subtleties that go unnoticed.
The Swiss, being Swiss; (read as a culture that is infatuated with cataloging time, money and doing things efficiently. i.e. Rolex, Swiss banks, Swiss army knives), created the Physilog III, a diagnostic tool filled with gyroscopes, and sensors that send real time data to the their
"... By strategically placing gyroscopes and accelerometers that relay real-time data back to the team on the poolside, the swimmer will get instantaneous data about his speed and coordination along with every other vital stat that will micro-manage his swimming style and help shave off that extra fraction of a second. And as we all know, that could well be the difference between a gold and a silver on an Olympic stage.
There has also been a special snorkel like device created that will measure the swimmers gas exchange ratio and help improve breathing technique as well. ..."