def calc_custom(custom, genome, scaffold, sequence, scaffold_coverage,
    total_bases):
    """
	custom = {(reads mapped to scaffold)/(total reads for sample)}/(length of scaffold)
	"""
    index = 0
    if scaffold in scaffold_coverage:
        if genome not in custom:
            custom[genome] = [[] for i in scaffold_coverage[scaffold]]
        for cov in scaffold_coverage[scaffold]:
            length = float(len(sequence[1]))
            bases = cov * length
            custom_value = bases / total_bases[index] / length
            custom[genome][index].append(custom_value)
            index += 1
    return custom
