The length of these pieces is represented by the spacing variable. If the user entered 400, these pieces would be 400 basepairs in length. One primer will be chosen from each of these regions. The user is allowed to enter minimum, optimal, and maximum values for the percentage of basepairs which are either G or C. Primer Annealing Primers also tend to dimerize and anneal to themselves. One method for accounting for this problem was developed by Hillier and Green, PCR Method.
Maximum values annealing between primers are able to be set by the user.