public double Calculate(Chain chain, Link link)
{
DnaProcessor.CheckDnaAlphabet(chain.Alphabet);
var a = remotenessCalculator.Calculate(chain.GetOrCreateCongenericChain(new ValueString("A")), link);
var t = remotenessCalculator.Calculate(chain.GetOrCreateCongenericChain(new ValueString("T")), link);
return (int)(a + t) == 0 ? 0 : (a - t) / (a + t);
}