BOINC's credit system is based on a 'reference computer' that can do

• 1 billion floating-point multiplies per second
• 1 billion integer multiplies per second
• 4 billion bytes per second of traffic to and from main memory (sequential, half reads and half writes)

Some BOINC projects grant credit only after results have been validated.

Each project maintains two types of credit:

• Total credit: The total number of Cobblestones performed.
• Recent average credit: The average number of Cobblestones per day performed recently. This average decreases by a factor of two every week, according to algorithms given below.

Both types of credit (total and recent average) are maintained for each user and host.

Leader boards

Possible future improvements

• Ideally, credit should reflect network transfer and disk storage as well as computation. But it's hard to verify these activities, so for now they aren't included.
• Eventually projects will develop applications that use graphics coprocessors or other non-CPU hardware. Credit should reflect the usage of such hardware. To accomplish this, we will need to let projects supply their own benchmarking functions. This will also handle the situation where a project's application does e.g. all integer arithmetic.

How 'Recent Average Credit' is computed

#define LOG2 M_LN2
    // log(2)
#define SECONDS_IN_DAY (3600*24)
#define AVG_HALF_LIFE  (SECONDS_IN_DAY*7)

// decay an exponential average of credit per day,
// and possibly add an increment for new credit
//
void update_average(
    double credit_assigned_time,        // when work was started for new credit
                                        // (or zero if no new credit)
    double credit,                      // amount of new credit
    double& avg,                        // average credit per day (in and out)
    double& avg_time                    // when average was last computed
) {
    double now = dtime();

    if (avg_time) {
        double diff = now - avg_time;
        double diff_days = diff/SECONDS_IN_DAY;
        double weight = exp(-diff*LOG2/AVG_HALF_LIFE);
        avg *= weight;
        avg += (1-weight)*(credit/diff_days);
    } else {
        double dd = (now - credit_assigned_time)/SECONDS_IN_DAY;
        avg = credit/dd;
    }
    avg_time = now;
}