The method used to identify the number of sets of chromosomes within a cell or organism (i.e. its ploidy). Each set is designated "n" so one set is n is haploid, two sets is 2n is diploid, three sets is 3n is triploid, four sets is 4n is tetraploid, etc. Also, 2n+1 is known as trisomy (i.e. two full sets plus a third copy of one of the chromosomes).