A parallel-line assay is the classical method to calculate a relative potency for a dilution assay. It is a linear fit which covers only the (near-) linear portion of the dose-response relationship without their asymptotes.
PLA 3.0 supports parallel line assays along with additional functionality to determine acceptable regions of the dose-response curve (configuration optimization).
The parallel-line method is a robust biostatistical analysis method based on D.J. Finneys Statistical Methods in Biological Assay, 3. edition, 1978. It is supported by the European Pharmacopoeia and the US Pharmacopeia.
PLA 3.0 allows you to carry out the regression for each standard/sample combination in your bioassay separately or at once.