### Generating - transformation of a time series variable

Hi all,

I have the following problem: I want to generate a new time series variable which measures the **accumulated** (the sum)of a variable "X", given a moving time **window** with a **constant** width of let say 40 years: The sum of the first 40 observations from time point t = 1 to t = 40 represents the first observation, the second observation is the sum of the observations from t = 2 to time point t = 41, the third observation is the sum of observation t = 3 to t = 42 etc. The constant time window of 40 years is moving by one step at the time. It's like a mowing average but **WITHOUT** dividing by the number of observations. I hope one of you Shazam experts could look into the problem - it would be of great help.

Regards,
P.