The forum karma system is designed to allow user moderation to a certain degree of posts in the forums. There are two main elements to the system. the base karma rating, and the per-post rating. Your base karma rating is your lifetime average of all ratings received starting from your 16th forum post. Your per-post rating is what people thought of that one particular post you made. Posts can be rated Either Up, or down. An Awful rating (red arrow) starts at a value of 1.00. After two Red arrows in a row, the next consecutive awful rating shows up as a -2.00. A fourth awful in a row goes back to 1.00. Basically every third consecutive awful rate on a post turns into a -2.00. That is the only time a negitive rate value actually affects base karma. A green arrow, or Excellent rating has a value of 6.00. It used to be possible for other rating values, however that functionality no longer exists. some older accounts do have ratings in the 2.00-5.00 scale too, but not in the last 4 years.
To rate a post, you press the red or green arrows located at the top right of each post. Anyone with a base karma score of 3.01 or higher can participate in the rating process. Under 3.01, or if the user has been "no rated" by an administrator the rate arrows are not available.
Users prior to 15 posts have no karma rating. This is to prevent "instant gurus" or "instant sub default" posters. On post 17 you start with a default base karma rating of 3.00. Each time you post, you automatically rate yourself two times at whatever your current base karma is at. To an admin, your rating when you post a thread looks like this:
Score: Decent [3.00]
Now lets say that a few users decided to rate your post.
Score: Decent [3.34]
That would make the per-thread rating 3.34. However your base karma would be the average of the 34 ratings you rated yourself as you posted (17 posts * 2 ratings at 3.00) and the four other ratings, which would leave you at a base karma of 3.05.
By achieving a base karma above 3.00, you will move up a rank, and are now a Scholar. There are three main forum levels:
Scholar - 3.01-3.65 - the majority of posters fall into this category
Sage - 3.65-4.39 - an exceptional poster, one who consistently provides good information and interacts well with the community. Rare to attain.
Guru - 4.40-5.00 - This poster participates above and beyond the call of duty. Their word is unquestioned, and in their area of expertise they are unparalleled. it takes a rare poster indeed to reach this rank.
Administrators - The forum administrators also have a custom colored title.
A post may still be rated when it is at either extreme of the scale. for example, on a post that has been rated to 5.00 that receives another excellent 6.00 rating, that 6.00 rating does count towards the posters base karma. Someone would then have to post additional 1.00 ratings to bring the entire post down too.
Rating guidelines: How and why you rate a post is your concern, however we ask that you keep a few things in mind. If you find yourself rating entire threads up or down, or following specific posters around and rating all of their posts one way, this is considered Karma camping, and is actively discouraged. Also, creating a secondary forum account for the sole purpose of buffering your own karma is considered cheating.
Karma reset button: Administrators have the ability to reset a user base karma to 3.00 if we feel the system has been systemically abused towards a given user. This is usually a one time event, and only if we feel the user has a particularily meritious case. We rarely even let the user know it has occured. This is to be used at the discretion of the administrator, and is not a "right" that a forum user can demand.
Admins also have no rate limiter, so we can append multiple up or down rates to a post as needed to adjust for system abuse if required. We rarely do so however. Administrator ratings to "nuke" a post show up as -50.00 and do not affect your base karma score in any manner.
I think that covers most of it.