How to find weber fractions from a confusion matrix

I have a confusion matrix for a 4 class classification problem which looks this:
View attachment 4672

My hypothesis is that group 3 is easiest to classify. Somebody suggested me that I can find weber fractions from this confusion matrix and perform further statistical analysis. I am unable to understand how I can do the same.

I am wondering if anybody can suggest me how weber fraction could be estimated or any other statistical test can be applied to this confusion matrix.

Thanks in advance.