(linear) interpolation if 3 ratios required - Phase 2

Original thread started here: (linear) interpolation if 3 ratios required?

Had a look at the example kindly provided by Fred Kohlhepp but struggling with a couple of things

I created a table of (real) data (well 3 sets of data anyway) (still too lazy..). Attached mcad sheet

1. What is the purpose of Matrix 'Mx' in Fred's example?
2. I can extract the data from the whole table but does one need to extract only the "lambda" (the final parameters based on ratios R1,R2,R3) for the interpolation

Thanks

Regards

JXB