lol, yah i did some hall experiments too recently, basically the field strength is a function of the distance to the magnet when this guy turns off:
it is a low gauss unipolar, though latching sounds like a better choice for position sensing generally. I have a large radius "magnet wheel" with strong magnets and should be able to get the sensor close so there doesn't seem to be an appreciable difference between the ON time and the OFF time with the unipolar in this instance though.
I spent a lot of time examining magnetic patterns on refrigerator magnets and etc with it
some more hall fun:
http://www.allegromicro.com/en/Products/Design/bipolar/