However the Nadi's are read by READERS who have trained years in reading ancient tamil and interpretting the writings written in poetic format correctly. This is where the readers experience matters. The nadi readers do not claim to be astrologers. At least the 3 readers I met. All the inputs you provide is in answering Yes or No to questions that you just know the correct answers for. No guessing, you just know these answers.

May I ask why would one not be certain of ones inputs?

I would think that if one cannot be certain of ones inputs, then the output would also be questionable. Such a person has a 'lot' to learn in this world so that their inputs are accurate.