SiteMeter does not currently track Unique Visits/Visitors. Our measurement is defined as a Visit. The basis of this measurement is calculated on a 30 minute time period, from the last page viewed (i.e. last activity seen).
As you are no doubt aware, a Unique Visitor is measured using a cookie (or other similar user hosted ID tag). This method permits one to measure hourly, daily, weekly, etc. unique visitors. You could even measure the number of unique over an entire year - which by the way will be an option for SiteMeter members in an upcoming new phase release. Of course there are limitations to this form of measuring traffic, not the least of which is people who disable cookies.
Our current method does not depend on Cookies to track visitor length, but like the cookie method does have inherent limitations. If a person visits a site and their initial record is cycled out of the visit details database (DB) before 30 minutes, they would be considered a new visit if they returned to the site, or if they were still on the site and clicked on another page. A site that cycles through its visitors quickly may not have reliable visit length data for the same reason.
However, it should be noted that the “Recent Visitors – By Details” report does not directly represent what is occurring in the DB. This report simply provides a sorted report of visitors to your site by visit time. These visitor records are updated as they move through the sorted By Details report. New arrivals normally appear in position 1 and slide down the report as newer visitors arrive.
What is actually happening in the DB is different than what you see in the By Details sorted report. In the DB new arrivals to your site are typically entered in the first line of DB. If a Visitor already in this DB record takes another action within your site they are moved to the top of the list. So the actual DB is sorted by Most Recent activity. Those who have not been active are eventually shifted to the bottom of the list and then purged.
In theory, someone sitting on a page of your site with a browser set to automatically refresh every five minutes would move to the top of the DB table every five minutes and would never drop off the list. The other thing to remember is that you are only considered a new Visit if your Last Activity was more than 30 minutes ago.
So, for a site with very high levels of Visit traffic it’s possible that a DB limited to approx 100 records would not contain enough entries to hold new visits and current visitor activity. In some cases this could result in current visits being dropped from the DB and then counted as new visits.
SiteMeter offers the option of having a larger visitor detail records with our Premium Account, which would resolve this issue. To those sites expecting large traffic volumes we recommend the Premium SiteMeter account.
As mentioned, in the coming months we’ll be launching a complete new site with new features, data points, and reports, which will include both our Current Visit methodology and the cookie base Unique Visitor counts. This will give our customers the option of examining both types of data.
Sincerely,
The SiteMeter Team