We have two charting solutions - the old RadChart and the new RadChartView. The new chartview is actually a set of controls - RadCartesianChart, RadPieChart, RadPolarChart and ChartDataSource. We strongly suggest you do not start new development with the old RadChart, but use only the new one.
I am a little unsure which of the two you use, so I will provide answer for the two. If you need further assistance, please confirm which control you are using.
The old chart has an additional-axes feature, which allows you to add an arbitrary number of additional axes. This is explained in our online help article here
The chartview has a multiple-axes feature (qsf examples here
, online documentation here
). This is a bit different. While the chart can work with more than one axis, each axis (except the main axis) needs to be associated with at least one series, in order to be added to the chart. For example, if you have only one series - you can have only one axis. If you have two series, you can have no more than two axes.
In cases, where you need to show two axes and a single series, we suggest you add a dummy series, which has no data. This dummy series will not be displayed, but you can use it in order to attach a new axis. You can then bind the min, max, step properties of this axis to the properties of the main axis.
I have attached a simple example that demonstrates both approaches.