To calculate the standard deviation of those numbers: 1  1. 2  Work out the Mean (the simple average of the numbers). 3  2. Then for each number: subtract the Mean and square the result.4  3. Then work out the mean of those squared differences.5  4. Take the square root of that and we are done!o calculate the standard deviation of those numbers: 1  1. 2  Work out the Mean (the simple average of the numbers). 3  2. Then for each number: subtract the Mean and square the result.
FBF = Flashback Friday. #FBF is an acronym primarily used on Instagram, Facebook, Twitter, and Tumblr that stands for Flashback Friday. Users typically use the tag on photos of moments in their past, like last yearâs vacation or a childhood friend.
This is in contrast to the mean time to failure (MTTF), which measures average time to failures with the modeling assumption that the failed system is not repaired (infinite repair time). The definition of MTBF depends on the definition of what is considered a system failure. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair.