GitHub's Historic Uptime
GitHub's Historic Uptime
Even better IMO is this status page: https://mrshu.github.io/github-statuses/
"The Missing GitHub Status Page" with overall aggregate percentages. Currently at 90.84% over the last 90 days. It was at 90.00% a couple days ago.
I think reasonable people can disagree on this.
From the point of view of an individual developer, it may be "fraction of tasks affected by downtime" - which would lie between the average and the aggregate, as many tasks use multiple (but not all) features.
But if you take the point of view of a customer, it might not matter as much 'which' part is broken. To use a bad analogy, if my car is in the shop 10% of the time, it's not much comfort if each individual component is only broken 0.1% of the time.