Why We Do Only A Half Revolution Around lord Shankara's Pindi OR Shivaling?

When we do pooja of  Shivaling, Gans (Followers) of Lord Shiva i.e. Rudragan or Pitrugan etc. are sit their to the mouth of shivaling for prashad.
If we do a full one revolution to Shivaling it will also for the Gans so that we have to do only a half revolution to Shivaling.