Today I used the LED readout to see Negative and Positive voltage using a rotation sensor. When I turn the rotation sensor counter clockwise, the LED readout flashes down negative voltage. When I turn the rotation sensor clockwise, the LED readout flashes up  positive voltage.

Here are two videos one of it going up and one of it going down:

https://drive.google.com/file/d/0BxN33tGWM_q5YWNxQkxtVzh0ZmNQSFF6Y01LUDgtbTV5UlB3/view?usp=sharing

https://drive.google.com/file/d/0BxN33tGWM_q5eW5SUjF0MkZnMjlkRVVhTS05UDZBamdZQnRJ/view?usp=sharing