This paper analyzes the use of Failsafing devices (or poka-yoke devices) for controlling processes that are managed using measurement control charts. We show that inspecting production for defects as work is completed (Shingo's self-checks) does not result in lower process variance. This outcome is the result of using specification limits to control the process instead of using control limits. If go/no-go inspections using control limits are used instead of specification limits for self-checks, information is lost as measurements are converted into binomial data. The ability to estimate the variance is reduced. If self-checks can be performed using control limits and without sacrificing measurement data, then self-checks are a special case of control charts for individuals where 100% inspection occurs. Using Source Inspection to inspect conditions for high quality production is shown to involve a binary decision, therefore source inspections using binomial data do not result in lost information. Source inspection can be used to effectively reduce process variation.