Precision 0.5 degree Stepper needed for Turntable
Belts or a gearbox are a good way to improve your resolution, but rather than relying on the stepper and a potentially sloppy coupling I suggest you include a rotary encoder (absolute or incremental, optical, hall, whatever). Couple that with a closed-loop position control algorithm (PID is easy enough in an MCU, or even an Arduino) and you can start to make some credible guarantees about turntable orientation.

Apart from the sloppiness inherent in soft couplings like belts, a good reason to do this is that steppers can jump steps, particularly if they're heavily loaded and having to fight a lot of inertia.  Unless you have a way of detecting this, you have no way of knowing that it has happened, let alone compensating for it.  otoh a closed-loop position controller will (if properly written &amp; configured) compensate for any mechanical slop, in either direction.