1. A machine method of TV picture motion measurement, comprising a first step of correlating first and second pictures to determine correlation as a function of selective displacement, thereby to determine a plurality of peak correlation values corresponding to respective motion vectors, and a second step of testing for each of a plurality of elementary areas of the pictures which of these motion vectors gives the best fit in deriving one of the pictures from the other, and wherein said second step comprises the following operations: (a) an elementary area of a picture is derived from said first picture using each of said motion vectors determined in said first step, thereby to form a set of derived elementary areas corresponding to said motion vectors respectively; (b) each derived elementary area is compared with the corresponding elementary error as a sum over the elementary areas of the magnitudes of the differences between corresponding points of said elementary areas; (c) that one of said motion vectors which results in the smallest comparison error is selected as giving the best fit in deriving said elementary area of said second picture from said elementary area of said first picture; (d) repeating operations (a), (b) and (c) for each of said plurality of elementary areas.