Could you please have a look at the attached file and let me know why I am getting different answers?
if the number in question is an input you I get the answer I am looking for, if the output is a result form say interpolation I will get wrong answer!!!
Why, this is happening, and how to overcome it?
This is an effect which you have to take in account when you are working with float numbers. Never compare float numbers for equality.
Its a roundoff effect. While the interpolated value R should be exactly 17.85 its actually slightly smaller - approx. -3.5*10^(-15). Evaluate R-Rd to see it yourself.