During a period of 35 years the authors have been active in promoting a technique with which the optimum ratio of the major plant nutrients N, P, S, K, Ca, and Mg can be calculated. In nutrientculture experiments in which each time the level of two of the nutrients is varied, two ratios of these nutrients are selected. With the yields obtained the ideal ratio of these nutrients is determined through graphical extrapolation. For each couple an optimum ratio is thus obtained, and through algebraic calculations the optimal ratio of the six nutrients is determined. The authors call this technique the “Method of Systematic Variations”. In a similar fashion, the optimal ratio of three nutrients can be calculated by means of extrapolation of data plotted in a triangle.