public override string ToString()
{
var sb = new StringBuilder("range ");
if (FromQuantity != null && ToQuantity != null)
sb.Append(FromQuantity).Append(" to ").Append(ToQuantity);
else if (FromQuantity != null)
sb.Append("MIN ").Append(FromQuantity);
else if (ToQuantity != null)
sb.Append("MAX ").Append(ToQuantity);
if (ErrorLimit != null)
sb.Append(" ").Append(ErrorLimit);
return sb.ToString();
}