Determine rc servo motor resolution
The servo you mention is a continuous rotation servo, which is really a bit of a hack - an aftermarket modification now being done for you at the factory or distributor.

These devices do not have a closed positioning loop - to the extent that they have proportional control at all, it's of speed or torque.  These are made by taking a normal servo design, and disconnecting the feedback potentiometer from the output shaft (or even substituting fixed resistors), so the internal positioning loop is opened and you get to control the apparent loop error by commanding a position different than the one it's feedback input is "stuck" at.  

I've not used this particular model, but those I have used had very poor control - there was very little input range between full-on in one direction and full-on in the other.  It's too bad someone doesn't make one with a closed velocity loop, though that would require a different motor technology or a rotation detection scheme (incremental optical encoder?  electronically commutated brushless motor?)