I recently read a paper by Watson and Harrison (1983) (see attached) and want to use the equation provided in their paper to reproduce their results by using their dataset. However, I have a trouble to calculate the M values (defined as "cation ratio M = (Na+K+2Ca)/(Al*Si)"). By using the exact same data in their paper, I cannot get the same M values as what they reported. In my calculation, I converted mass percentage of each element to mole and then use the M equation. I am wondering is this correct?

For example using their Run No.1:

SiO2 54.2 wt.% Si 0.902 mol

Al2O3 16.9 wt.% Al 0.331 mol

CaO 7.6 wt.% Ca 0.136 mol

Na2O 2.3 wt.% Na 0.074 mol

K2O 0.8 wt.% K 0.017 mol

So M = (0.074+0.017+2*0.136)/(0.902*0.331)=1.21 But in their paper it is 1.89

Thanks.