http://burp.renderfarming.net/forum_thread.php?id=2101

A while ago BOINC changed the credit granting algorithm from the original BOINC credit algorithm to CreditNew. CreditNew has a fairly complex way of calculating just how much credit should be granted for every workunit. It also has the unfortunate assumption that either the workunit workload is known in advance OR said workload does not change too much from workunit to workunit, across applications and so on.
BURP has crazy freakout monster workunits intermixed with tiny workunits - and even uses the same application for those WUs. We have almost no clue how long a workunit will take until it has been rendered, even within a single session the workunits may be different in length by several orders of magnitude.
At first it was assumed that CreditNew would eventually settle. However, over time, it has become increasingly clear that CreditNew does not perform well for the kind of workload, applications and situation we have here at BURP - in fact the credit system has become the target of much ridicule and confusion.

Payday:

"Payday" is a development subproject of BURP. The main objective is to retroactively perform a correction on all granted credit since the introduction of CreditNew and subsequently replace or accompany CreditNew as the main credit granting algorithm for BURP. Secondary objectives are to make it way simpler to understand than CreditNew, make it credit-stable both in short-term and long-term measurements and at the same time make it fairly transparent to the community what is going on.

It will never be perfect, but it will very likely become a bit better than CreditNew.

The basic way that credit will be calculated with Payday is this:
Amount of work done per hour * hours it took * cobblestone factor = your credit
Oldschool BOINCers will find this very similar to the original credit system - and this is no coincidence since that system served as inspiration for Payday.

Payday, as stated above, is still under development, but a large part of the algorithm framework is already in beta testing at the moment.

[Example provided in the thread]