In StarGate, each use of the gate requires 7 chevrons – 6 for the points in space and a 7th for point of origin.

In “Fifth Race,” O’Neill modifies the gate dialing program to travel to the Othalla in the Galaxy Ida. This required the use of an 8th Chevron. The 8th chevron is also needed to travel to Atlantis from Earth (and vice versa).

The were scenes cut from “The Shrine.” These contained information on the 9th chevron. These were removed since this contains details in StarGate Universe (possibly the next stargate movie). The idea is that when the Ancients were heading into a new area of space, they could send a ship ahead and seed the new frontier with stargates. This ship would have a gate with a 9th chevron.

What’s odd about this is that the 8th Chevron is already supposed to be the ‘area code’ of another gate system. So why need a 9th? What occurred to me is that maybe the 9th chevron controls which universe to go to. Instead of just being another galaxy, what if the 9th chevron can access other realities. We already know Merlin played with moving his research of sync to hide it from the other ascended beings. Another possibility is that the 9th chevron allows access to all area codes. This would allow the dialer to find the stargate on the ship regardless of where it is currently located.

The current idea is that a group from Atlantis gates to the exploration ship and gets stuck in a far off area of space with no way to return.  Kind of reminds me of StarTrek Voyager.