Bitlog uses a 'trick' to obtain information, by placing a 1x1 pixel image but actually extracting information because the image reference is a php program or including a php file.

There are 2 kinds of possibilities.
-Information comes from a PHP page
   -we know the refering page (if not blocked).
   -we know the requested page.
-Information comes from a HTML page
   -we know requested page.

-In all cases we can determine browser-agent

The browser agent is used to determine whether a robot 'crosses' our website.
If the user cannot be found in the cookies, place a cookie and mark time/ip/agent.
If the user is found, check whether the same page is requested within the 'no-register' time,because it is a page refresh or so.
If it is a new page, add the page with the cookie number.
Every visit is registered this way.

The method used by bitlog is very accurate, but requires every page on the site to have the reference to bitlog via the <img src=bit.php .......> reference, or better the include 'bit_include.php' statement in the top.
BiTLOG works with caching systems without any problem.
Make sure the caching statement comes AFTER bit_include.php!

For the country references BitLog uses a quite big table. This table has to be updated from time to time. It contains about 2 billion ip addresses and 62000 records (as per 2004).
Use the information from any site that has this info readily available, like www.ip-to-country.com.
Obtain the delimited version. See readme for instructions.
How long to keep data? Since bitlog logs every page visit the table migh grow huge after a long time.
It is not advisable to keep the data longer than 2 years. The admin section lets you delete the old data.
Make sure you backup your database on a regular basis.
Table updates can be uploaded as .gz file, and will be expanded on the server.
We try our best to update the downloadable ip-to-country file as often as possible.

Pageviews and Usersonline can be requested with bit_include.php only.
For pageviews put $pageview=0 and for usersonline put $useronline=0 in the heading before calling bit_include.
The made-up layout will be in $pageview1 and $useronline1.

If you are unsure about certain data, you can write all data to a text file on the server.
Uncomment in bit_include the lines below:
// test write to bitlogtest.txt file for testing purposes only
//*************
A txt file named bitlogtest.txt will be created and contain date/time referer etc.
This is helpfull if you are unsure about certain data, agent data for sample.

You will need the bandwidth package and access to you Apache log files.
The files can be rotated by Apache or you can do it with calcband_logrotate.php.
Automatic roration can be achieved with PHPJobScheduler, do it on the low hours.
Error log is a great help for tracing errors you otherwise cannot find, like jscript errors in preloading pictures, not found style sheets and javascripts.
And of course unauthorized acces and trying to enter the site.