Time To Hello World: If the average time is 50 seconds with a standard deviation of 40 seconds and the target time is 80 seconds we get a z-score of (50-80)/40 = -.75. The -.75 is a z-score and we convert it to a percentage (which is the area under the curve up to -.75 standard deviations) and we get .2266. We subtract this value from 1 (because we want times to be less than the spec limit) which generates a percentage of 1-.2266 = 77.3%
Completion Rate: If 8/10 developers completed the goal, the completion rate is 80%.
Error Avoidance Rate: If 3/10 users report errors, the error rate is 30%.
Happiness (CSUQ): An average score of a 5.6 on a 7 point scale with a standard deviation of 2 becomes (5.6-5)/2 = .3. The .3 is a z-score and gets converted into a percentage =61.7%.