From Unofficial BOINC Wiki
A term meaning the amount of effort contributed by a user to the BOINC Powered Projects that that Participant is supporting. It is a metric that allows Participants to monitor their individual contributions. Credit is gained through the following mechanism:
- Each Work Unit may be sent to several computers.
- When a computer reports a Result, it claims a certain amount of Credit, based on how much CPU Time was used.
- When sufficient Results have been returned (number set by the Project as the minimum Quorum Size), the Validator compares them. If the Results agree, they form the Quorum of Results - once the Quorum of Results has been created, users are granted Credit based on the Project rules and the Claimed Credit values. The complete rules are below.
Please keep in mind:
- There may be a delay of several days between when your computer reports a Result and when it is granted Credit for the Result. Your User page shows you how much Credit is "Pending" (claimed but not granted).
- The credit-granting process starts when your computer reports a Result to the Scheduling Server (not when it finishes computing the result or uploading the Result Data Files to the Data Server).
- In rare cases (e.g. if errors occur on one or more computers, your return comes in after the Quorum of Results has been established, or none of the Results match, etc.) you may never receive Credit for the computation of a Result.
- The Credit accumulated while a member of a Team will be added to that Team's Total Credit, a Participant leaving a Team does not change the Team's Total Credit; except for Climateprediction.net (CPDN) which uses the old SETI@Home Classic rule where the Team's Total Credit is a simple summation of the Total Credit earned by the Participants that are a member of that Team.
 Credit Granting Process
The basic process looks something like this:
The Validator has a queue. So all the returned Work Units are standing in a line, waiting to be validated. For the sake of this example, let's pretend the Validator runs through one Work Unit per day, and has 20 Work Units in the cache. So, it'll look something like this:
So, 2 weeks into the project, you still haven't gotten any Credit, but you get to read on the Forums how everyone else is getting thousands of Credits every day. However, notice that your Work Unit is still in the cache, and getting closer to the front. Therefore, your Credits will come, as soon as they're worked through the line. Not only that, they'll start coming on a regular basis since they started joining the queue on a regular basis.
(And yes, this is a simplistic version of what happens, but it illustrates the point.)
 Credit Granting Rules
These are the standard rules for granting Credit, based on the number of Results returned. Each Project will decide which rule is appropriate for their Project, or if they need to rely on a different method.
|1||The Claimed Credit is granted provided the Result passes some Project specific test.|
|2||The lowest of the Claimed Credit values is granted.|
|3|| The top and the bottom of the Claimed Credit values are removed and the middle value is granted.
|4 or more||The top and the bottom of the Claimed Credit values are removed and the middle values are averaged and the average of these Claimed Credits is granted.|
One of the points that causes confusion is the fact that a Project like SETI@Home may issue more work initially than is required to satisfy the Quorum of Results. In this case, it is possible for the Quorum of Results to be established before all of the Results have been returned.
 Credit And Teams
Credit as it applies to a Team works on a simple rule. While you are a member of a team all the Credit that you earn is also added to the Total Credit of the Team. When you quit, your earned Credit is no longer added to the Team's Total Credit balance. The Team does not lose the Credit from their Total Credit equal to your earnings.
 Team Credit Example
Now you want to be part of a Team. So you join a Team, where you start to accumulate Cobblestones from zero for that Team. While a member of this Team you accumulate 2,000 Cobblestones. At this time you have 4,000 Cobblestones Total Credit, while the Team has the same 2,000 of your Cobblestones added to their Total Credit.
You then get it into your head that another Team is better, so you quit the first Team and join the other. You start with zero Cobblestones at this Team. You now accumulate another 2,000 Cobblestones. By this time you have 6,000 Cobblestones, the old team has 2,000 of your Cobblestones and your new Team has accumulated the same additional 2,000 Cobblestones.
Cobblestones will always stay with the individual. But to prevent team-hopping as happened in SETI@Home Classic, where people would take 2 million "credits" from one team to another, if only for a week, then hop back, this rule has been changed for the whole of BOINC.
- Much of this behavior was done to coerce the Team into doing something that the, um, "big-shot" wanted even though the rest of the Team was against the change. In other words, "do it *MY* way or I will take my credits and you will lose your standing ...".
 Project Specific Rules
A few of the BOINC Powered Projects have special rules for the granting of credit. These rules are based on the needs of the Project and are not likely to become "standard" rules for the BOINC System, but, do allow the Project to meet their specific needs.
Participants that returned identical Results will get same amount of Credit, which is an average of the Claimed Credit when lowest and highest value are ignored. In most cases this is the median of the Claimed Credits. This Credit is called "canonical credit".
If Work Unit has 10 Successful Results but there are not enough identical Results to form a Quorum of Results, the Results are granted points according to how well they match with the other Results. The best-matching Results will receive the median average of Claimed Credits (calculated in same way as the canonical credit). Other Results will get Credit proportional to the canonical credit and the Result's match points. Although Participants get Credit from these kind of Results, the Results are not used in the physical studies.
Please note that different CPU architectures may yield different Floating Point results. This is especially true between Pentium and Athlon XP CPUs. Although differing Results are not used in physical studies, they may still be useful to us in finding possible problems in our software. Of course, this requires that the CPU used for calculations doesn't produce real errors. This can happen especially on Over Clocked CPUs. Even if the Over Clocked system seems to work fine (maybe an unexplained crash once in a month or so) it might skip one bit in one of the 10^14 floating point calculations commonly done in a Work Unit, producing a highly different end result. Such a bad Result will actually cause gray hairs to us, so if you have Over Clocked CPU and get lots of Invalid Results, consider lowering the clock speed or detaching from the Project.
 Also See
- Claimed Credit
- Computation of Credit
- Data Quality
- Granted Credit
- Pending Credit
- "Pending Credit" Page
- Recent Average Credit
- Reporting Process
- "Result" Page
- "Results For Computer" Page
- "Results For User" Page
- SETI@Home Data Integrity
- Total Credit
- Redundancy and Errors
- Homogeneous Redundancy
- Redundancy Checker
- Quorum of Results