A forecasting model has produced the following forecasts:

$\backslash$table$[[$Period$,$Demand,Forecast Error$],[$January$,120,110],[$February$,110,115],[$March$,115,120],[$April$,125,115],[$May$,130,125]]$

At the end of May the tracking signal would be

MAD$=\frac{|D_t-F_t|}{n}$

Cumulative error

$E={\displaystyle \underset{?}{\overset{?}{}}}{e}_t$

Tracking signal $=\frac{{\displaystyle \underset{?}{\overset{?}{}}}(D_t-F_t)}{\text{M}\text{A}\text{D}}=\frac{E}{\text{M}\text{A}\text{D}}$

The use of Excel$($r$)$ is allowed for this problem.