* Gabriel, K.R. (1971). «The biplot graphic display of matrices with application to principal component analysis». Biometrika. 58 (3): 453–467. doi:10.1093/biomet/58.3.453
Lewi, Paul J. (2005). «Spectral mapping, a personal and historical account of an adventure in multivariate data analysis». Chemometrics and Intelligent Laboratory Systems. Chemometrics and Intelligent Laboratory Systems. 77 (1-2): 215–223. doi:10.1016/j.chemolab.2004.07.010