One more thing... the description of the "notifiers out" indicator (which is shown in the context menu when you hover over the indicator) states: "notifiers out is the entire array of notifiers in, unless an error occurs. If an error occurs, notifiers out contains only those notifier refnums that caused the error." However, this is not the actual (or the desired, IMO) behavior. If some notifiers are received before the error occurs (for example, if one notifier becomes invalid after others are received), then the notifiers and notifications received should be output to "notifiers out" and "notifications" (respectively). I don't think that it is entirely possible to know which notifiers caused the error, since the "Wait on Notification from Multiple" primitive does not tell you which notifier generated the error. We could infer which notifiers caused the error by checking if any of them are Not a Refnum. But, in any case, the user of this VI could make this check, themselves, if an error did occur. If this VI does actually need to output an array of notifiers that caused the error, then I would prefer if this were an additional output ("notifiers with errors") and we used "notifiers out" to contain the notifiers that were actually fired.