WPF Graph - AxisDateTime with AbsoluteTimeStamp

Hello,

I am trying to plot a few Observable Collection to Graph with AxisDateTime.

Graph:

<ni:Graph x:Name="Graphs_HPT_Temperature" PreferIndexData="False" RenderMode="Raster" Margin="10,10,10,10" Interactions=""><ni:Graph.Axes><ni:AxisDateTime Location="Near" Label="Time (s)" Orientation="Horizontal"><ni:AxisDateTime.MajorDivisions><ni:RangeLabeledDivisions TickMark="Rectangle"/></ni:AxisDateTime.MajorDivisions></ni:AxisDateTime><ni:AxisDouble Label="Temperature (°C)" Orientation="Vertical" Range="0, 100, System.Double"/></ni:Graph.Axes><ni:Graph.Plots><ni:Plot Label="Temp 1"><ni:PlotRendererGroup><ni:LinePlotRenderer Stroke="IndianRed"/><ni:PointPlotRenderer Stroke="Black" Fill="IndianRed"/></ni:PlotRendererGroup></ni:Plot><ni:Plot Label="Temp 2"><ni:PlotRendererGroup><ni:LinePlotRenderer Stroke="DimGray" /><ni:PointPlotRenderer Stroke="Black" Fill="DimGray"/></ni:PlotRendererGroup></ni:Plot><ni:Plot Label="Temp 3"><ni:PlotRendererGroup><ni:LinePlotRenderer Stroke="Blue" /><ni:PointPlotRenderer Stroke="Blue" Fill="LimeGreen"/></ni:PlotRendererGroup></ni:Plot></ni:Graph.Plots></ni:Graph>

I am defining source of data like this (all three data sources - randValues, randValues2 and randValues3 - are ObservableCollection<double> :

Graphs_HPT_Temperature.Data[0] = randValues;
Graphs_HPT_Temperature.Data[1] = randValues2;
Graphs_HPT_Temperature.Data[2] = randValues3;

ObservableCollections are filled with data every second. The following picture describes my problem, when I am using AxisDateTime, the showing date is relative (starting from 1.1.0001) and not absolute. How can I get the absolute date (timestamp) on my AxisDateTime?

I know I can use Waveform structure for these, but when the ObservableCollection contains more than 1000 samples, I need to delete first sample of the collection. Unfortunately, Waveform contains only Append function.

Thanks for your answer.