WTMADs are calculated as follows:
WTMAD = [2.7 X 165 MAD(MB08-165) + 2.8 X 99 X MAD(W4-08) +
2.0 X 36 X MAD(G21IP) + 2.4 X 25 X MAD(G21EA) +
1.6 X 12 X MAD(PA) + 2.4 X 11 X MAD(SIE11) +
4.5 X 26 X MAD(BHPERI) + 3.2 X 76 X MAD(BH76) +
3.0 X 30 X MAD(BH76RC) + 4.4 X 43 X MAD(RSE43) +
2.2 X 6 X MAD(O3ADD6) + 3.1 X 25 X MAD(G2RC) +
7.1 X 7 X MAD(AL2X) + 6.8 X 6 X MAD(NBRC) +
2.9 X 34 X MAD(ISO34) + 4.1 X 9 X MAD(DC9) +
6.2 X 14 X MAD(DARC) + 12.9 X 6 X MAD(IDISP) +
2.8 X 27 X MAD(WATER27) + 11.7 X 22 X MAD(S22) +
13.8 X 10 X MAD(PCONF) + 3.5 X 15 X MAD(ACONF) +
5.2 X 17 X MAD(SCONF) + 5.0 X 10 X MAD(CYCONF)]/2682.5
More information can be found in: L. Goerigk and S. Grimme in J. Chem. Theory Comput 2010, 6, 107-126.