I was able to accomplish my desired labels by using the FillSceneGraph event, and created my new labels like this

 aLabel - new label (new Point(aComputedXal, aYStartingval + mChart.Axis.X.Extent), string "label");

 some of the properties I suggested can be used to force the axis minimum to be a certain time, which can be rounded to the hour or half-hour:

Axis.X.RangeType = Custom

Axis.X.RangeMin = DateTime.Parse("1/1/2001 2:00:00 AM").Ticks;

Axis.X.RangeMax = DateTime.Parse("1/1/2001 4:00:00 AM").Ticks;

as for the tooltip getting values from another column... to do this you need to create a class that implements the IRenderLabel interface.  You can store a copy of your DataTable as a private field on an instance of this class, and use it to output the tooltip string, something like this:

string IRenderLabel.ToString(Hashtable context)

{

 int dataRow = int.Parse(context["DATA_ROW"].ToString());

return this.myTable.Rows[dataRow]["FullDateTimeString"];

}

While I haven't tried this yet, I was able to get some sort of markings from the labels automatically, but I want them every half hour, on the half hour, which was the problem I was having, i think the code you gave me will work the same as what I was seeing, it would label the very first poing on the x-axis regardless of time and every half hour thereafter, I want it to ignore all points except for the hours and half hours exactly.  Will the code you sent me accomplish this?  Secondly I also need some help with tooltips.  I have a LineChart, with my data loaded into a DataTable with two columns, one for the DataPoint, and one for the DataTime (which is being stored AS a DateTime)... I want my tooltip to show up as follows

(DataValue, HH:MM:SS)

 I get the following (DataValue, FullDateTimeString) (i.e. 3.4, 2/17/09 12:00:00)

 Currently my tooltip formatstring is listed as <DATA_VALUE:0.00,#,##>, \n <SERIES_LABEL: T>

What am I doing wrong and how can I accomplish the desired tooltips?

 a small one.  FillSceneGraph runs each time the chart is painted, but then again so does the normal labelling code.

Thanks, I might have to try your answer, do you think there'd be a performace hit using fillscenegraph versus using the properties of the axis?

 glad to hear you found a solution.  alternatively, if you have a true DateTime axis, you should be able to set TickmarkInterval = 30, TickmarkIntervalType = Hours, TickmarkStyle = DataInterval, RangeType = Manual, RangeMin = DateTime.Today.Ticks, RangeMax = DateTime.Today.AddHours(3).Ticks using the axis properties.