Realm searches your data nightly looking for possible duplicate profiles.
Duplicates can be introduced either by manually entering similar records twice, or by importing records when similar ones already exist. You can see a list of possible duplicate profiles on the Overview dashboard. Also, there is a button on the Info tab of each duplicate profile. Once you locate duplicates, you can merge, delete, or ignore them.
When you import profiles from other programs or spreadsheets, they are also searched for duplicates. Realm compares the information in your profiles and determines the probability that two are duplicates based on the amount of matching data in them.