Lisa is comparing q uarterly sales values of last 4 quarters in term of actual and forecast values. She finds the tracking signals are consistently...

Lisa is comparing quarterly sales values of last 4 quarters in term of actual and forecast values. She finds the tracking signals are consistently coming out as large negative numbers (i.e., -7.5, -7.1, -8.8, and -10.5). What should she do with the forecasting model?