public static Tolerance CalculatePrecursorMassError(double theoreticalMass, double observedMass, out int nominalMassOffset, out double adjustedObservedMass, double difference = Constants.C13C12Difference,
ToleranceUnit type = ToleranceUnit.PPM)
{
double massError = observedMass - theoreticalMass;
nominalMassOffset = (int) Math.Round(massError/difference);
double massOffset = nominalMassOffset*difference;
adjustedObservedMass = observedMass - massOffset;
return new Tolerance(type, adjustedObservedMass, theoreticalMass);
}