I'm using the NDataSeriesDouble.Add(DateTime value) method since my data is in DateTime format.  On this Axis I need to add a NAxisConstLine which doesn't take a DateTime which is what my data is in.  How do I calculate the appropriate double value for the DateTime I have for my const line?

I've worked around this by inserting the double I'm looking for and then calling NDataSeriesDouble.GetDoubleValue(0) to get the double value then clearing and filling my series.  This is not ideal and I suspect I just can't find how to do something that seems is obviously needed.  I looked around but I would appreciate knowing how to do this.