If you're not using a power meter and tracking your watts, then you're giving the competition an advangage. SRAM's Quarq Quatro Power Meter integrates into the crank spider for easy installation, low weight, and minimal maintenance. It's ANT+ wireless compatible, enabling you to use the head unit of your choice (sold separately), and it has no wires or external sensors, which means that your beautifully sleek machine stays clutter-free. Since the power sensor is in the crank, you can easily switch wheels for race day. Other nice features include an easily replaced battery (no overnight charging!) and a wattage reading accuracy of +/- 2%. Also, calibration values are stored in the Quatro so there's no need to re-calibrate if you switch head units.