Hello everyone, thanks all in advance for any comments and help.

I have been asked to create a spread sheet for work that tracks the number
of customers that come into our buisness througout the 24hour day, recored
the number of customers and then create a rolling three week average. an
examble of this would be monday april 18th 10 people were in the store,
monday april 25 5 people came into the store and moday may 2nd 10 more people
came into the store so the average of this is 3..were my problem is I need a
way to automatically drop april 18th out of the equation when i put in the
data for may 9th? is there a way to automatically do this?
again thanks in advance
Aaron