How to find non-stoichiometric ratio

rpestana94

I'm reading a paper "Photocatalysis-mediated drug-free sustainable cancer therapy using nanocatalyst", here the authors synthetise nanoplates of SnS_{1.68}  with nanodots of WO_{2.41}.

The authors said the valence state for Sn are: Sn^{4+}:Sn^{2+} = 0.681:0.319  so the non-stoichiometric ratio is Sn:S = 1:1.68.

For the WO, the valence state are W^{6+}:W^{5+}:W^{4+} = 0.307:0.216:0.477  so the non-stoichiometric ratio is W:O = 1:2.41.  

I would like to know where 1.68 and 2.41 come from.

Thanks in advance.