Service Records - The "Duration" Field

The "Duration" field in a service record is an estimate of how long work took to complete.

It's

done - start

where

done
is right now for open records, or the date the work was last recorded as done in some way.
start
is the planned start date, if there was one, otherwise it's the date the record was created.

When specifying this field in a customized sort or display, use the name "duration".