It should be pretty far down their list of priorities at this point, but I just noticed the "Exception Percentage" value at https://status.github.com/graphs/past_day is saying 483.704%. The fact that they're measuring this in percentages implies the maximum is 100%, but this isn't so.
I imagine it was a percent measured against successful responses. The exceptions now far exceed those successful responses. You are correct in saying it should be 100% but people have a habit of scaling beyond it.
If this is in fact how they're measuring...I was going to make this post a long rant about how ridiculous it is to measure it in that way, but then I realized that people do sometimes measure probabilities by quoting the win-to-loss or loss-to-win ratio.
This is called "odds" and frequently used in gambling. Usually, though, someone says "4.7 to 1" or "47 to 10" (abbreviated 4.7:1 or 47:10) instead of 470%. Usually the larger number is stated first, and the direction is usually indicated by a word like "favorite" or "longshot." So one would say "Errors seem to be a 4.7:1 favorite today."
It's slightly complicated by the fact that odds can measure one of several things:
A. A probability ratio ("Red" is a slight underdog in the game of roulette [1]; the odds against hitting it are 20:18 since there are 20 non-red spaces and 18 red spaces)
B. A payout ratio ("Red" pays 1:1, meaning the prize if you win this bet is equal to the amount of the bet)
C. The current payout of a paramutuel pool [2]
Odds are seldom used outside of a gambling context.
