1. Van der Akker, J. A., Lathrop, A. L., Voelker, M. H. and Dearth, L.R., Tappi J. 41(8):416(1958).
2. Duncker, B. and Nordman, L., Pap. Puu 47(10):539(1965).
3. Retulainen, E., Niskanen, K. and Nilsen, N., Paper physics, Fapet Oy, Finland, p.55 (1998).
4. Mark, R. E., Handbook of physical testing of paper, Vol. 1, Marcel Dekker Inc, New York, p.727 (2002).
5. Cowan, W. F. and Cowdrey, E. J. K., Tappi J. 57(2):90(1974).