Hi Fabio & Girish,
There are two issues on the histogram chart being discussed here.
1. Negative values in the histogram chart-
As you know, Histogram chart counts the no. of records against the distinct values and provides the output as a bars with count of the records for those values.
This is the expected functionality out of the chart and it is working as expected in your case. All you need to do is validate the values as per the process requirements and remove the invalid values at transaction or query level.
Also striking a process orientation through established SoP(Standard operating procedures) wil ensure such invalid value wont occur any more.
2. Bar width can be fixed using the Histogram Cell Count parameter in the Parameters tab of the iSPCChart configuration.
So by adjusting the width of the chart at HTML applet parameters and the histogram cell count parameter using the java script function "iSPCChart.getChartObject.setHistogramCellCount(int)', you can set the bar width.
With regards,
Ponilango