WTMADs are calculated as follows:
WTMAD = [445.5 X MAD(MB08-165) + 222.75 X MAD(W4-08) +
72.0 X MAD(G21IP) + 60.0 X MAD(G21EA) +
19.2 X MAD(PA) + 26.4 X MAD(SIE11) +
117.0 X MAD(BHPERI) + 222.75 X MAD(BH76) +
90.0 X MAD(BH76RC) + 150.5 X MAD(RSE43) +
13.2 X MAD(O3ADD6) + 77.5 X MAD(G2RC) +
49.7 X MAD(AL2X) + 62.4 X MAD(NBPRC) +
98.6 X MAD(ISO34) + 72.6 X MAD(ISOL22) + 36.9 X MAD(DC9) +
86.8 X MAD(DARC) + 15.0 X MAD(ALK6) + 222.75 X MAD(BSR36) +69.0 X MAD(IDISP) +
75.6 X MAD(WATER27) + 222.75 X MAD(S22) +
96.6 X MAD(ADIM6) + 22.2 X MAD(RG6) + 114.8 X MAD(HEAVY28) +
138.0 X MAD(PCONF) + 52.5 X MAD(ACONF) +
88.4 X MAD(SCONF) + 50.0 X 10 X MAD(CYCONF)]/3091.4
More information can be found in: L. Goerigk and S. Grimme in J. Chem. Theory Comput 2011, DOI: 10.1021/ct100466k.