Calculate difference between every other time record

Question

Here's what I have going on.  Users are keeping track of time they work on a project.  Data to be used in contained in two columns.  In the first column they enter "start" or "stop".  In the second column they input the date and time.  So, output would look something like this:
start     1/1/2011 3:30pm
stop     1/1/2011 3:35pm
start     1/2/2011 1:00pm
stop     1/2/2011 1:30pm
start     1/2/2011 2:00pm
stop     1/2/2011 2:18pm
I need to be able to calculate the difference between the start and stop time and then create a running total of those time.  Running total not an issue but what can I do to calculate the time difference between start and stop?  Been awhile since I used Crystal (about 5 years) so I've forgotten way too much.  Another issue that I'm running into is that sometimes the users forget to enter the start or stop, so I might have two stops in a row (with one missing the start time) or two starts in a row.  I'm not completely sure how I want to handle those yet.  I may just throw those records out but not certain how I'll do that yet.
Sorry if this is a bit basic.  Trying to relearn Crystal again - oh, and it's crystal reports 10.

Answer 1

Here are a couple of formulas that should help you out.
This will calc the time diff between sequential start and end times
WhilePrintingRecords;
Global DateTimeVar x := IF {TableName.Type} = "start" THEN {TableName.TimeStamp} ELSE x;
Local DateTimeVar y := {TableName.TimeStamp};
Local NumberVar z:= IF {TableName.Type} = "start" THEN 0 ELSE DateDiff("n", x, y);
And this one will provide a manual running total
WhilePrintingRecords;
Global DateTimeVar x := IF {TableName.Type} = "start" THEN {TableName.TimeStamp} ELSE x;
Local DateTimeVar y := {TableName.TimeStamp};
Global NumberVar z:= z + IF {TableName.Type} = "start" THEN 0 ELSE DateDiff("n", x, y);
Note that you'll want to sort  the records by the "TimeStamp"
HTH,
Jason