Every innovation in Quarq’s next-generation DZero platform is channeled into DFour. It embodies 10 years of Quarq technology advances with new features such as dual Bluetooth low energy & ANT+ wireless data transfer, the new Qalvin BLE app & compatibility with BB30 bottom brackets. Quarq power meters use their patented direct-force technology to precisely measure your physical performance throughout your ride. Their meter is located in the crankset, the heart of the bicycle, & because it gathers data from both legs, & it's located at the precise point where muscle energy is converted to forward movement, the power meter spider is the most accurate place to gather power data. 10K Temperature Compensation Eliminates variables caused by heat & cold to provide an unwavering record of your performance through all conditions. Built to Last An IPX7 waterproof rating, an easy-to replace CR2032 battery, a 2-year warranty, free firmware updates & acclaimed worldwide support. Easy to Use Manual & automatic zeroing make Quarq power meters truly set & forget. The chainrings are replaceable should your bike, discipline or ability change. Qalvin BLE with Bluetooth For i OS & Android. With any phone you can set zero offset, check battery, run diagnostics & update firmware. Free. Other Features DFour also features Omni Cal (change chainrings without affecting accuracy) & Ax Cad (accelerometer cadence – no magnet).