"Nederland, Indexen van de Archieven, Primaire Archiefstukken (BS en DTB), 1600-2000," database,
FamilySearch (
https://familysearch.org/ark:/61903/1:1:QL44-P9FT : 22 August 2017), Frederika Balk, Birth 04 Mar 1863, Groningen, Nederland; from database,
openarchives (https://www.openarch.nl : 2016); citing Groningen, archive 1399, inventory number 6101, record number 195; ; AlleGroningers.