$C = 12.01;
    $O = 16.00;
    $N = 14.01;
    $H = 1.01;
    $P = 30.97;
    $water = 18.015;

    $adenine = 5 * $C + 5 * $N + 5 * $H;
    $guanine = 5 * $C + 5 * $N + 1 * $O + 5 * $H;
    $cytosine = 4 * $C + 3 * $N + 1 * $O + 5 * $H;
    $thymine = 5 * $C + 2 * $N + 2 * $O + 6 * $H;
    $uracil = 4 * $C + 2 * $N + 2 * $O + 4 * $H;

    $ribose_phosphate = 5 * $C + 7 * $O + 9 * $H + 1 * $P;      #neutral (unionized) form
    $deoxyribose_phosphate = 5 * $C + 6 * $O + 9 * $H + 1 * $P;

    # the following are single strand molecular weights / base
    $dna_A_wt = $adenine + $deoxyribose_phosphate - $water;
    $dna_C_wt = $cytosine + $deoxyribose_phosphate - $water;
    $dna_G_wt = $guanine + $deoxyribose_phosphate - $water;
    $dna_T_wt = $thymine + $deoxyribose_phosphate - $water;

    $rna_A_wt = $adenine + $ribose_phosphate - $water;
    $rna_C_wt = $cytosine + $ribose_phosphate - $water;
    $rna_G_wt = $guanine + $ribose_phosphate - $water;
    $rna_U_wt = $uracil + $ribose_phosphate - $water;

    $dna_weights = {
        'A'             => [$dna_A_wt,$dna_A_wt],            # Adenine
        'C'             => [$dna_C_wt,$dna_C_wt],            # Cytosine
        'G'             => [$dna_G_wt,$dna_G_wt],            # Guanine
        'T'             => [$dna_T_wt,$dna_T_wt],            # Thymine
        'M'             => [$dna_C_wt,$dna_A_wt],            # A or C
        'R'             => [$dna_A_wt,$dna_G_wt],            # A or G
        'W'             => [$dna_T_wt,$dna_A_wt],            # A or T
        'S'             => [$dna_C_wt,$dna_G_wt],            # C or G
        'Y'             => [$dna_C_wt,$dna_T_wt],            # C or T
        'K'             => [$dna_T_wt,$dna_G_wt],            # G or T
        'V'             => [$dna_C_wt,$dna_G_wt],            # A or C or G
        'H'             => [$dna_C_wt,$dna_A_wt],            # A or C or T
        'D'             => [$dna_T_wt,$dna_G_wt],            # A or G or T
        'B'             => [$dna_C_wt,$dna_G_wt],            # C or G or T
        'X'             => [$dna_C_wt,$dna_G_wt],            # G or A or T or C
        'N'             => [$dna_C_wt,$dna_G_wt],            # G or A or T or C
    };