How come the "Optimouse" library is not working for me?

I'm using "Optimouse" as downloaded here, GitHub - zapmaker/OptiMouse: Optical mouse sensor library for Arduino 1.x by Martijn The
I'm using the ADSN2051 sensor, and I am running the coordinates example in optimouse.
I have changed the import statement to match my sensor. And I'm pretty sure, I've connected it right.
When I run It, the output almost constantly decreases, with some changes when I move the mouse.

Some of the output would be like:
"x=-753587 y=-7859
x=-753664 y=-7971
x=-753868 y=-7963
x=-754021 y=-8075
x=-754190 y=-8043
x=-754374 y=-8171
x=-754655 y=-8170
x=-754998 y=-8296
x=-755122 y=-8287
x=-755465 y=-8285
x=-755733 y=-8252"

How can I fix this to actually track the mouse.