code: private void trackingStopMenuItemActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_trackingStopMenuItemActionPerformed
          if (trackingWorker != null) {
              trackingWorker.cancel();
          } else {
              assert(false);
          }
      }
docs: GEN-LAST:event_trackingStartMenuItemActionPerformed