On this site, the resolution numbers have been collected at different times from different individuals, and in order for the data to be meaningful, a uniform testing procedure has been established.
Resolution is measured at wide open and at all full f-stops thereafter, both in the center and in the corner. The file res.txt contain the detailed resolution data as well as resolution averages. The averaging is done by weighing all f-stops equally and center resolution twice as heavily as that at the corners. For zooms, the above calculation is performed at the widest, middle and longest focal lengths, and is then averaged to a single number.
For ease of comparison, each lens' overall resolution average is also reported in the lens specification tables.
Note that the averaging is done in an Excel spreadsheet, and you can modify the weights and calculate other results that better suit your needs.
Resolution is only one measure of optical quality, but many argue that it is the most important one. Other criteria not considered at this site at this time include field curvature, coma, chromatic aberration, proneness to flare, and many others.
You are encouraged to submit resolution tests from your own lenses. You must be willing to spend some time with setting up carefully, measuring distances, etc. And you must spend a bit of money for film and development. Read the testing procedure carefully, and setup your equipment exactly as described. Shoot the required number of frames, and calculate the final results. Repeat this with as many lenses as you are willing to test, and send me the results.
The raw resolution numbers for each lens are either from a single test or averages from multiple tests. Therefore your contributions are valued and will be included even for lenses that have already been tested.