Kramer and Sandor 126), 127 described a variant on the precision point technique which they call selective precision synthesis (SPS). It relaxes the requirement that the curve pass exactly through the precision points by defining accuracy neighborhoods around each point. The size of these tolerance zones can be different for each point, and more than nine points can be used. They point out that exact correspondence to a set of points is often not necessary in engineering applications and even if achieved theoreti cally would be compromised by manufacturing tolerances