I am trying to calculate how many minutes pass between when I start a task and when I complete it.

 

I have two timestamp fields:  start & stop.

They are populated with a script that inserts current time into each field upon clicking the start-stop button.

 

The calculation is as follows:

 

Case (  not IsEmpty ( Stop Time );(Stop Time - Start Time);"" )/60

 

This works fine as long as all of the hours occur within the same day.

As soon as the clock hits midnight, however,  the elapsed time becomes a negative value.

 

How should I express the formula?

 As soon as the clock hits midnight, however,  the elapsed time becomes a negative value.

 

Not if you are really using timestamps.

 

And you can just write 

Case (  stop ; ( stop - start ) / 60 )

have two timestamp fields

They are populated with a script that inserts current time into each field

 

 Make sure they are indeed timestamp fields, and let the script populate them with the current timestamp, not current time.

Thanks guys.  Problem solved.