BIRT- methode : can't call or retrieve a data element in Chart API

Hi everyone,
I'm working on a report using BIRT where i need to retrieve a value of a data element (stored in a table) in chart script, spicifically in beforeGeneration() , and use for setting the step size dynamically.
I've tried something like:

params["step"]=this.getRowData().getColumnValue("Max-min/10"); ** //i called first the data element from the table and saved it in a parameter**
unction beforeGeneration( chart, icsc )
{

importPackage(Packages.org.eclipse.birt.chart.model.data.impl);
importPackage(Packages.org.eclipse.birt.chart.model.attribute.impl);

xAxis = chart.getBaseAxes()[0];
yAxis = chart.getOrthogonalAxes( xAxis, true)[0];
xscale =xAxis.getScale();
yscale = yAxis.getScale();

xscale.setStep (icsc.getExternalContext().getScriptable().getParameterValue("step")); ** //getting the parameterValue**
}

Unfortunatelly, the chart API does not identify the methode getParameterValue after getScriptable(). I believe this is because the getParameterValue() belongs to the **reportContext ** interface which i can't use in beforeGeneration().

I'm using the ALL-in-one version 4.8.0 and eveything seems to work properly.

So is there anyway that i can get the this data element from my dataset in my chart script?.