The Maintenance Ratio metric, which appears in the Isolation Cost and Time Statistics section of the Fault Isolation Report, is a measure of the maintenance manpower burden required to maintain a system.
In order for this metric to be accurate as a prediction, test times and object replacement times must be entered in terms of total maintenance time (e.g. man-hours). It will not be accurate if test or object times are entered in terms of clock/calendar time. For example, if it takes three maintainers 2.5 hours on the clock to replace a component, the replacement time for that component should be set to 7.5 hours (the number of maintenance man-hours) if the Maintenance Ratio is to be used as a prediction. Note: Because the Inherent Availability metric is based on clock/calendar time, these two metrics will not be accurate as predictions within the same eXpress report. Of course, both metrics can always be used as an aide to optimizing a diagnostic design (provided they are not both used as predictions of system behavior under maintenance), regardless of the terms in which time attributes have been defined.
