Right now, if you want to represent a dataset to scale, the only (very difficult - haven't succefully done so) way is to do this is a Timeseries graph.
In the ad-hoc custom properties, the documentation states that the xAxis.type can have the following values: Can be one of "linear", "logarithmic", "datetime" or "category", but it seems like the linear scale is NOT supported.
Components | JasperReports Server, UI/UX, AdHoc |