[EricH]

Originally Posted by Alex.q

Why do 2 wheels make it more more accurate? Also, would a wide roller serve the same purpose as 2 large wheels, or do you need 2 separate pts of contact?

2 wheels give a bit of a groove for the ball to "settle" into, resulting in the ball leaving from the same place every time (and thus having exactly the same spin every time). It's not really an accuracy aid, but a precision aid. A single wheel may have the tendency to let the ball slip sideways to one direction or the other, causing less-predictable spin.

A single wide roller could act like one wheel or two, depending on exact construction--with a shallow groove in the middle, or a groove/depression on the compression bar/hood, it'll act like 2; if neither has that, there's no telling. It might act like 1 or 2 wheels.