>Thank Al for your reply.
>I believe that I correctly did not explain myself what I want is subtraction or to add two hours for example:
>12:00:00 p.m. - 9:0:00 is equal to 3 hours.
>I mean the intensity is make a form to calculate the extra time the my employers work, for example:
>Peter Mckarly work the saturday, June 23 from 8:00: a.m. to 12:00:00 p.m.
>In the form the user has to put the Peter id the date (Saturday, June 23) and in a grid the start to (8:00:00 a.m.) Finish to (12:00:00).
>I hope you can help and thanks again.

You are currently using separate grid fields for the date, and the time(s)? I'd suggest using DateTime fields, which include both the date and the time in a single field e.g. 06-25-2001 11:54:00. If you don't care about the seconds portion you can SET SECONDS OFF.

You could initialize the date portion with DATE() to save typing.

The point of my earlier message is that by using DateTime fields/variables, you can get results like

lnHours = (ltDateTime2 - ltDateTime1) / 3600