“UNIQUE” HITS: Reader Steve Furlong says my counter is understating the traffic:

The “unique visitors” counter is only an approximation of the actual unique visitors you get. It almost certainly counts distinct IP addresses. This doesn’t quite map to distinct end-user computers because of IP masking, Network Address Translation (NAT) and a couple of other things. Stripping the jargon, AOL and other large ISPs and most largish companies are assigned blocks of IP addresses. Smaller sites might have just a single address but support multiple users with internal routers.

A user visiting you from one of those sites will seem to you to have one of the IP addresses in that block; if he visits again he might have the same or a different apparent address. And someone else visiting your page from one of those systems might be assigned the same address.

Two concrete examples, showing each of these distorting factors:

– My web server’s log sometimes shows someone visiting some of my pages. It’s clearly the same person visiting successive pages, but he might show six different IP addresses for ten hits in five minutes. (My site normally gets a few hundred hits per *week*, discounting the robots, so I can examine the logs in detail if I wish.)

– My small home network connects to the internet with a DSL line with a static address. I have a router to support up to four simultaneous connections, but they all appear to be the same address so far as the world is concerned.

You might well know all this, but I find it’s better not to assume that people in other fields know the stuff in my field of work, and to “waste” the time explaining.

Yes, I’m familiar with this stuff, though many readers may not be. And my counter’s worse yet, because it only counts visitors to the main page — links to individual posts go elsewhere and don’t get counted. But nonetheless it’s shown more unique visitors than I expected, so it’s taught me something. And by making it available, I want to undermine those people who have occasionally implied that bloggers lie about their traffic. I’d like to see some “mainstream” sites provide similar information in a similar fashion, but I doubt that will happen.

Comments are enabled on this one. What do you think?