The sites page
Every address this account serves, each with a status, the round-trip time in milliseconds, and what your browser has recorded about it before.
What a check does
The request goes from your browser to the site and the time it takes is measured with the same clock as everything else on the page. That part is straightforward.
The other part is not, and the page says so rather than implying more than was measured. The request is sent in a mode that does not permit reading the reply, so the status code is hidden. Answers therefore means the address took the connection and replied with something — not that it replied with 200. A 404 page or a 500 page still counts as answering. Only a refused connection or a timeout reads as no answer.
There is a six-second timeout on each check. Checks run one after another rather than all at once, so a slow third site does not make the first two look slow.
The history column
Each result is written to this browser's local storage: forty checks per site, and nothing older than seven days. From that the page derives how many checks there have been, how many answered, and the median time.
This is yours alone. It is not sent anywhere, and clearing site data clears it. It is also only as good as your own connection — a history of failures here usually means your network, not the sites.
The bar under each site
A rough proportion, not a scale. Anything under a second fills it and anything slower drains it, because the difference between 300 ms and 900 ms is not what a reader is looking for. The number beside it is the real figure.