The ODE file is specified below followed by a plot showing the least squares fit using assumed values of p, q, and m. Three ODE files follow with their respective least square plots and are based selected periods of the data. For the time frame consisting of data from Jan '87 through Dec '89. For the time frame consisting of data from July '88 through June '90. For the time frame consisting of data from Jan '90 through Aug '92.
Sales seem to drop off through the spring and summer.