This floating window is presented when you select "Contest Helper..." from the Log Menu.
The Contest Helper Window has two main sections - the K5ZD Call Completion table and the Duplicates table. These two tables are updated dynamically as you type a call into MLDX - not waiting for a lookup.
"Super check partial is a feature that K1EA first introduced in his CT logging software. It enables the use of a database to extend the list of calls that appear in the check partial call window. Used correctly, it can help you more quickly pull a call out of the QRM. Used incorrectly, e.g. to guess calls, it can result in stupid mistakes and significant score reductions. Caveat emptor!" - Randy Thompson, K5ZD
Details on the latest files here. If you want to update these files, MacLoggerDX looks for them in the data/scp folder.
The Duplicates table is a user-configurable dupe checking tool that will check duplicate QSO's in your log based on date and time, band, mode and exact match.