As pictured the formula calculates a one-step-ahead forecast of the
intercept term with a factor loading of all previous complete observations.
Choosing the desired regression function and removing the "$"
before the row numbers allows the estimation of rolling regression statistics.
Repeat the formula to recursively update the forecast or roll the regressions.
If forecasting, compute the forecast as shown below.
Alternatively, we could have used FORECAST as the regression function
with "B24" as the x input and the known_y’s and known_x’s
as specified in step 2.