sentences:  Traditional standards conversion techniques adopted interpolation as a way to cater for the differences between line resolution and field frequency.What the original BBC converter tried to do (using the limited technology of the day) was to minimise judder by choosing either one 50 Hz field or a 1/2-1/2 mix of two 50 Hz fields, whichever was "nearer" to the temporal position of the target 60 Hz field.This gives a sequence like this (Nx = 60 Hz field x, Py = 50 Hz field y)