Difference between the M7 and M8 coprocessors?

What's the difference between the M7 and M8 coprocessors? I've been unable to find a clear answer online. On the iPhone 6 webpage, Apple simply states: > When you’re in motion, the M8 motion coprocessor continuously measures > data from the accelerometer, compass, gyroscope, and a new barometer. > This offloads work from the A8 chip for improved power efficiency. And > now those sensors do even more, measuring your steps, distance, and > elevation changes. Is the only difference the ability to track data from the new barometer?