code: public void setXValues(double xOffset, double xInterval) {
      // Update the x-values according to the offset and interval.
      xValues = new Object[zValues[0].length];
      for (int i = 0; i < zValues[0].length; i++) {
        xValues[i] = xOffset + (i * xInterval);
      }
    }
docs: Sets the x-values which are plotted along the x-axis. The x-values are calculated based upon
  the indexes of the z-values array:
  
  <pre>
  
  {@code
  
  <pre>
  x-value = x-offset + (column-index * x-interval)
  
  </pre>
  
  
  } *
  </pre>
  
  <p>
  The x-interval defines the gap between each x-value and the x-offset is applied to each value
  to offset them all from zero.
  
  <p>
  Alternatively the x-values can be set more directly with the <code>setXValues(Object[])</code>
  method.
  
  @param xOffset an offset value to be applied to the index of each z-value element.
  @param xInterval an interval that will separate each x-value item.