Dear Peter, For the tests I was doing, I was using 500 Monte Carlo simulations. Are the errors in the file attached to https://gna.org/task/?7180 those which are different? 500 sims should be sufficient for accuracy to a few decimal places. The steps you describe are the same as what relax does. It's a bit strange that there are differences. The Monte Carlo sims in the PDC and relax, if using the same peak heights and errors should converge to the same results. Do you have another PDC file with error that I can used to re-run MC sims? The values and errors I obtain from the latest file is below. Regards, Edward # mol_name res_num res_name spin_num spin_name value error None 2 Gln None N 2.1931543671 0.0150953094197 None 3 Ile None N 2.33146407173 0.0160577446857 None 4 Phe None N 2.3482964848 0.019713488727 None 5 Val None N 2.2490812645 0.0164275028474 None 6 Lys None N 2.27941978889 0.015118434456 None 7 Thr None N 2.21973220186 0.0142724888389 None 8 Leu None N 2.24024670209 0.0220723067644 None 9 Thr None N 1.9682398599 0.0320202880659 None 10 Gly None N 2.08801972269 0.0133512466715 None 11 Lys None N 1.99776427143 0.0119683402446 None 12 Thr None N 2.16448623389 0.0174891646325 None 13 Ile None N 2.27255388183 0.0203045621019 None 14 Thr None N 2.19928611083 0.0137179789481 None 15 Leu None N 2.27943290864 0.01841703596 None 16 Glu None N 2.08711900135 0.0110867843226 None 17 Val None N 2.28472626854 0.0149813716965 None 18 Glu None N 2.10803348086 0.0165871439247 None 20 Ser None N 2.24335721396 0.0136423661701 None 21 Asp None N 2.3491468761 0.0123466109271 None 22 Thr None N 2.27508355307 0.0179254994426 None 23 Ile None N 2.46729511309 0.022032166148 None 25 Asn None N 2.39562318634 0.0182835550536 None 26 Val None N 2.13340147848 0.0124491345714 None 27 Lys None N 2.36258684463 0.021452496764 None 28 Ala None N 2.38480717279 0.0167515948037 None 29 Lys None N 2.32696831127 0.0186312168945 None 30 Thr None N 2.42063807895 0.016486280768 None 31 Gln None N 2.37225963882 0.0145645530678 None 32 Asp None N 2.34327154101 0.0141218929004 None 33 Lys None N 2.1927627806 0.0133120293255 None 34 Glu None N 2.23809535599 0.0144347657445 None 35 Gly None N 2.2461346515 0.0122274121117 None 36 Ile None N 1.99122925973 0.010910732682 None 39 Asp None N 2.29368330103 0.0126561091892 None 40 Gln None N 2.25464084772 0.0146681195393 None 41 Gln None N 2.22441709558 0.0180042863108 None 42 Arg None N 2.28040886598 0.0226407473358 None 43 Leu None N 2.17231047053 0.0237437949291 None 44 Ile None N 2.27954369008 0.0201909508149 None 45 Phe None N 2.26618944243 0.0208950941528 None 46 Ala None N 2.17293180472 0.0496094013897 None 47 Gly None N 2.19171718851 0.0143718164149 None 48 Lys None N 2.20180904452 0.0159731114836 None 49 Gln None N 2.11417079383 0.0137897460469 None 50 Leu None N 2.24457803209 0.0193730177104 None 51 Glu None N 2.13348726698 0.0178416908891 None 52 Asp None N 2.0460014256 0.0130027410002 None 54 Arg None N 2.19214984513 0.0173101801326 None 55 Thr None N 2.27509231624 0.0229093320248 None 56 Leu None N 2.36912374644 0.0178696073777 None 57 Ser None N 2.29814984784 0.0129737044328 None 58 Asp None N 2.37723175535 0.0159530364094 None 59 Tyr None N 2.22560065336 0.0147756564606 None 60 Asn None N 2.28460144064 0.0121672447449 None 61 Ile None N 2.34228508004 0.0180155615894 None 62 Gln None N 1.97375590837 0.0127517602123 None 63 Lys None N 2.16513054478 0.00997271942879 None 64 Glu None N 2.31915705344 0.0199426460098 None 65 Ser None N 2.18919504068 0.0149076372426 None 66 Thr None N 2.1815681959 0.0155283232121 None 67 Leu None N 2.26786646063 0.0200115697764 None 68 His None N 2.24651038599 0.0204872753534 None 69 Leu None N 2.24847954259 0.0171435701978 None 70 Val None N 2.31549239579 0.0204085987616 None 71 Leu None N 2.17566168322 0.0141512899583 None 72 Arg None N 2.1637210197 0.0124881076678 None 73 Leu None N 1.85663248042 0.00972554000058 None 74 Arg None N 1.61255064461 0.0109491376192 None 75 Gly None N 1.16260116356 0.0127191083108 None 76 Gly None N 0.763062241201 0.00312485609259