The Aggregate M indicator is based on the concept that in the long term the market trends, while in the short-term the market is noisy, and has a tendency to mean-revert. Why not combine the two concepts to keep life simple? The Aggregate M is supposed to reflect an adjusted median that is filtered for short term noise. The median is a far more accurate measure of central tendency than a simple average especially with noisy data. Taking a superior measure of trend and filtering out some of the noise by adjusting for short-term mean reversion creates an even better median. The Aggregate M is now both trend and mean-reversion rolled into one.

Full details here

Note: I have changed David's variable names and used percentage values instead of decimals.
Please read the comments within the code itself.