I solved this using two variables that checks for "higher/lower value then already defined" in the loop that creates the xml file. After the loop and before output, i added 1.25m to the values. The below code result i.e. -1143 and 42542.
if (row.value.Value < _getLowestValue) { _getLowestValue = row.value.Value; }
if (row.value.Value > _getHighestValue) { _getHighestValue = row.value.Value; }_floorRoof =
"yAxisMaxValue='" + _getHighestValue.ToString("#") + "' yAxisMinValue='" + _getLowestValue.ToString("#") + "'";
this.lGraph.Text = string.Format(strXmlHeader, xmlGraphData, _floorRoof);
It might help someone..
//J