(linear) interpolation if 3 ratios required?

To all

I am sure I have seen discussion on the topic in the past but my search drew a blank. I am looking for the "best" method to interpolate a value when 3 ratios are required to get to the value desired, see attached doc for extract of table I am working with

steps are

1. establish ratio 1 (R1 = m1/m2)
2. establish ratio 2 (R2 = I1/I2)
3. establish ratio 3 (R3 = L1/L2)
4. with this 3 ratios get value lambda

as you can see if any of the ratio is between know values, one needs some kind of interpolation. So the question is how doe some approach this?

Thanks

Regards

JXB