Hi, welcome to the cache checker. This is a script which will update a particular, non-CGI, file. By looking up this file you can then decide if the cache in your browser is working correctly, or if it is using its cached copies regardless of the changes the server reports.
Note that it is quite possible that some of the software between your cache and the file, including proxy servers, TCP stacks, and the web server itself, are buggy. Don't assume the problem is your end. I would love to hear of any bugs you discover (particularly if they are with this script or the Apache server serving the file in question).