Maybe it would be better to measure uptime not as what percentage of time the site is up, but instead as how likely a randomly selected visitor is to be able to access the site.

That would adjust for the fact that the window of peak demand, e.g. the US workday, which is when Github tends to go down, is also when people need the service the most.

[1]: https://mrshu.github.io/github-statuses/