system
Given the following post, respond as if you're commenting on Reddit:
human
[Stargate/SG1]What was the benefit of having to manually lock the 7th chevron?

Why are the addresses 7 digits long if a particular gate would always have the same last digit?  Why wasn't it just assumed, or are there other possible functions than point to point transport that could be accessed via last chevron manipulation?
gpt
In  one book, they could be locked on the lines between chevrons for off-planet, interstellar locations.  So if you are moving a gate by a ship the last chevron changes.

8th chevron dialed another galaxy (Atlantis)

9th?  who knows?