system
Given the following post, respond as if you're commenting on Reddit:
human
[StarGate] Why does the 7th chevron need to be explicitly entered?

As far as I understand, the 7th chevron-the origin-never changes. And even if it does, it's not up to traveler to change it. The variables are only the target coordinations, but the origin is constant. It basically has zero entropy. Why doesn't the gate calculate it internally? What's the purpose of entering it manually? Has there ever been a case, where a gate was activated with different glyph than its origin?
gpt
Once they discovered 8 and 9 chevron addresses, this becomes clearer.  The origin chevron is used to initiate the dialing.  If the origin chevron is the 7th chevron, the gate knows you're dialing a gate in the Milky Way.  Otherwise, you would be dialing a gate much farther away, and would require much more power.