It's not possible to predict with precision or certainty how long a specific power supply will operate or after how many hours it will fail. However, users can determine expected lifetime or likelihood of failure with high confidence using probability measures and techniques. A supply's reliability is a function of multiple factors: a solid, conservative design with adequate margins, quality components with suitable ratings, thermal considerations with necessary derating, and a consistent manufacturing process. Using the formula of e to the negative lambda t, users can calculate that the probability that a component with an intrinsic failure rate of 10-6 failures per hour wouldn’t fail after 100,000 hours is 90.5%, after 500,000 this decreases to 60.6% and after 1 million hours of use this decreases to 36.7%. An adaptation of this formula can also be used to calculate the effect of redundancy within a system or the system as a whole.