Getting it centered properly is pretty easy - there is a hole where the bolt goes through and its pretty easy to estimate where to glue the motor on over the hole.  If you wanted to get technical you could trace out the exact diameter of the motor and draw a line around the central point.  The wobble in mine in the video was due to me pulling the plastic cover off the motor and not being back on properly (ie: in and out, not off centre from the saw mounting position).  This is just noticeable but does not worry me at all.