A method of calibrating a polynucleotide sequencing process, comprising: i) making one or more artificial polynucleotide sequence comprising: retrieving a natural nucleotide sequence, and reversing the natural nucleotide sequence, wherein the reversed sequence has the same nucleotide bases in the same order as the natural nucleotide sequence, wherein the order of the nucleotide bases is in the 5' to 3' direction in the natural nucleotide sequence and in the 3' to 5' direction in the reversed sequence, wherein the artificial polynucleotide sequence comprises at least 100 nucleotides, wherein any 100 contiguous nucleotides of the artificial polynucleotide sequence have less than 100% sequence identity with any known naturally occurring genomic sequence of the same length, and wherein the artificial polynucleotide sequence is a DNA sequence; wherein the one or more artificial polynucleotide sequence comprises: (a) one or more features of naturally occurring eukaryotic chromosomes selected from the group consisting of gene loci, introns, exons, CpG islands, mobile elements, repetitive polynucleotide features, small scale genetic variation and large scale genetic variation, (b) one or more features of naturally occurring prokaryotic chromosomes, or (c) one or more features of naturally occurring viruses, phages or organelle sequences; ii) adding the one or more artificial polynucleotide sequence to a sample comprising a target polynucleotide sequence to be determined, iii) determining the sequence of the target polynucleotide; iv) determining the sequence of the one or more artificial polynucleotide sequence; v) comparing the sequence determined in iv) to an original sequence of the artificial polynucleotide sequence; vi) determining the accuracy of the sequence determination in iv) based on the comparing in iv); and vii) calibrating the sequence determination in iii) using the accuracy determined in vi). i) making one or more artificial polynucleotide sequence comprising: retrieving a natural nucleotide sequence, and reversing the natural nucleotide sequence, wherein the reversed sequence has the same nucleotide bases in the same order as the natural nucleotide sequence, wherein the order of the nucleotide bases is in the 5' to 3' direction in the natural nucleotide sequence and in the 3' to 5' direction in the reversed sequence, wherein the artificial polynucleotide sequence comprises at least 100 nucleotides, wherein any 100 contiguous nucleotides of the artificial polynucleotide sequence have less than 100% sequence identity with any known naturally occurring genomic sequence of the same length, and wherein the artificial polynucleotide sequence is a DNA sequence; wherein the one or more artificial polynucleotide sequence comprises: (a) one or more features of naturally occurring eukaryotic chromosomes selected from the group consisting of gene loci, introns, exons, CpG islands, mobile elements, repetitive polynucleotide features, small scale genetic variation and large scale genetic variation, (b) one or more features of naturally occurring prokaryotic chromosomes, or (c) one or more features of naturally occurring viruses, phages or organelle sequences; retrieving a natural nucleotide sequence, and reversing the natural nucleotide sequence, wherein the reversed sequence has the same nucleotide bases in the same order as the natural nucleotide sequence, wherein the order of the nucleotide bases is in the 5' to 3' direction in the natural nucleotide sequence and in the 3' to 5' direction in the reversed sequence, wherein the artificial polynucleotide sequence comprises at least 100 nucleotides, wherein any 100 contiguous nucleotides of the artificial polynucleotide sequence have less than 100% sequence identity with any known naturally occurring genomic sequence of the same length, and wherein the artificial polynucleotide sequence is a DNA sequence; (a) one or more features of naturally occurring eukaryotic chromosomes selected from the group consisting of gene loci, introns, exons, CpG islands, mobile elements, repetitive polynucleotide features, small scale genetic variation and large scale genetic variation, (b) one or more features of naturally occurring prokaryotic chromosomes, or (c) one or more features of naturally occurring viruses, phages or organelle sequences; ii) adding the one or more artificial polynucleotide sequence to a sample comprising a target polynucleotide sequence to be determined, iii) determining the sequence of the target polynucleotide; iv) determining the sequence of the one or more artificial polynucleotide sequence; v) comparing the sequence determined in iv) to an original sequence of the artificial polynucleotide sequence; vi) determining the accuracy of the sequence determination in iv) based on the comparing in iv); and vii) calibrating the sequence determination in iii) using the accuracy determined in vi).