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[Nitrus]

Here's a full run-down of levels:

Recruit - Default group for everyone
Junior Officer - Requires 20 posts
Officer - Requires 50 posts
Senior Officer - Requires 150 posts
Executive Officer - Requires 500 posts
Section Chief - Requires 1000 posts, 5 rep & 6 months registration
Legend - Requires 5000 posts, 15 rep & 1 year registration