3) n-chi tartibli interpolyatsion splaynni defekti orqali aniqlanadi. N-chi tartibli interpolyatsion splaynni defekti 1ga teng diyiladi.
Agarda m=n-1 bo’lsa ya’ni (n-1)=1 interpolyatsion kubik splaynni ta’rifi va defekti haqida defekti 1ga teng bo’lgan interpolyatsion kubik splayn diyiladi.