Motion vectors record the "distance" between two areas on screen based on the number of pixels (also called pels). MPEG-1 video uses a motion vector (MV) precision of one half of one pixel, or half-pel. The finer the precision of the MVs, the more accurate the match is likely to be, and the more efficient the compression. There are trade-offs to higher precision, however. Finer MV precision results in using a larger amount of data to represent the MV, as larger numbers must be stored in the frame for every single MV, increased coding complexity as increasing levels of interpolation on the macroblock are required for both the encoder and decoder, and (minimal gains) with higher precision MVs. Half-pel precision was chosen as the ideal trade-off for that point in time. (See: qpel)