Process Downtime Level measures the extent to which an operational process is available and running.
Process Downtime Level = (TA t / PPT t) x 100
PPT t is the Planned Productive Time that a process should be available in a given time period t.
TA t is the actual productive time that a process has been available in a given time period t.
This indicator is included in the book: Key Performance Indicators - the 75+ measures every manager needs to know, which contains an in-depth description of this KPI, as well as practical advice on data collection, calculations, target setting, and actual usage.