You appear to have this relationship:
Invoices::Invoice Id = LogBook::related inv id
After you perform a find on LogBook, you want to use that found set to find all records in Invoices that are not linked to a record in the current found set in LogBook.
Use Go To Related Records with the match found set option to pull up a found set of records in Invoices that link to at least one record in your found set in LogBook. Then use Show Omitted Only to swap the found set of those records that match for all the other records in your table--the records that do not match to a record in your found set in LogBook.
Great thanks !!! That's exactly what I was trying to do.
When you said use "Go To Related Records", I wasn't sure if you meant in a script or if that was a menu option but I found it as a script step and so I created a one line script using that with the "Match all records in current found set" option. and it worked great. I then wanted to narrow the search more so I was able to go into find mode and use "constrain found set" to get exactly what I needed.