This is the official resource for the Enneagram Graphic created by Nik Helbig in 2014. Do download the .pdf file. Included in the pdf is the bibliography.
Downloading the file and getting to the bibliography on the last page is recommended for anyone interested in learning where the information of the work comes from.Helbig_Enneagram_graphic
Analyzing Enneagram by Observing the Talking Style