Can it be used as an encoder to tell the rotation of the gear it’s mounted for? Also these seem to be what FIRST has given us. However the image doesn’t seem to show what we actually have. Is that exactly what FIRST gave us or would we need something else.
From my experience, these will only give a count, not direction. That doesn’t mean you can’t derive direction from another source, hint, hint, hint. 
So from counting teeth we could derive the # of rotations? We should already know the direction from what we are telling the robot to do?
Thank you for the help.
Anyone know if the link in my first post is the sensor that they gave us?
You don’t necessarily know the direction that the motor is spinning. As a first approximation, you do, but when you are reversing direction, or being pushed, you can be applying power to have the motor go one direction and actually have the wheels, and therefore your encoders, be spinning in the other direction.