1. Harrison, Wilson R., Suspect Documents (New York: Frederick A. Praeger, 1958), p297.
2. Hecker, Manfred R., The Change of Handwriting as a Process of Identification. Presented at themeeting of the International Association of Forensic Sciences (Bergen, 1981).
3. Osborn, A. S., Questioned Documents. 2nd ed. (Albany: Boyd PrintingCo.1929), pp151-166.
4. The Influence of Writing Instruments on Handwriting and Signatures
5. Effects of Writing Instruments on Handwriting Details