1. http://www.fischer-technology.com/fileadmin/user_upload/default/Brochures/en-gb/BROC_Probes_902-111_en.pdf
2. http://www.pfonline.com/articles/coating-thickness-measurement-the-fundamentals
3. http://www.iacs.org.uk/document/public/Publications/Resolution_changes/PDF/REC_087_Rev2_pdf2592.pdf