Comparison of Two Distinct BBN Codes
  This paper compares the results of two SBBN codes developped independently by different teams of physicists. These two codes have significant differences that lead to a discrepency between their final mass fractions of Helium-4 of 0.003. This paper shows that the mass fractions of each code had different orders of convergence, and how the number of timesteps affects the accuracy of the mass fractions. At the end, the paper shows how to modify both codes so that their Helium-4 mass fractions agree to around 0.0001. 
Juan F. Lara (Center for Relativity, University of Texas at Austin)