What exactly is meant by "corrected” MXD," you ask? Outstanding question -- and the answer appears amorphous from program to program. Indeed, while some employ one or two of the aforementioned "corrections," others throw everything but the kitchen sink at the raw data prior to output.

For instance, in the subfolder "osborn-tree6mannoldprog," there’s a program (Calibrate_mxd.pro) that calibrates the MXD data against available local instrumental summer (growing season) temperatures between 1911-1990, then merges that data into a new file. That file is then digested and further modified by another program (Pl_calibmxd1.pro), which creates calibration statistics for the MXD against the stored temperature and "estimates" (infills) figures where such temperature readings were not available. The file created by that program is modified once again by Pl_Decline.pro, which "corrects it" – as described by the author -- by "identifying" and "artificially" removing "the decline."

But oddly enough, the series doesn’t begin its "decline adjustment" in 1960 -- the supposed year of the enigmatic "divergence." In fact, all data between 1930 and 1994 are subject to "correction."

And such games are by no means unique to the folder attributed to Michael Mann.