The Omnium Over-Drive has an internal progressive resistance. The faster your rear wheel spins the more resistance you will get. You can see in the resistance chart as your rear wheel speed increases so does the resistance. If you would like to reduce the resitance you can simply switch to an easier gear which will reduce your rear wheel speed.
This data was based on a 150lb rider riding on a standard road bike with 700x23 tires at 100 psi. Changing the rider weight, tire size, or tire pressure will change the resistance curve.