It all starts with the data.

This newsgroup provides support for Microsoft Access, the relational
database.  What system is your library using?

Regards

Jeff Boyce
Microsoft Office/Access MVP

Hi

Create a table with with time in time out fields and link it to the book
table rimary field.

You would not need to "do" anything when the book was taken out just add an
AfterUpdate event to the normal process and use this to add Now() to the
In/Out table