A simple mathematical relationship amongk-class estimators is demonstrated when a regression equation in a simultaneous system involves the regression of an endogenous variable (y0) on exogenous variables (x1, …,xλ) and on a single endogenous “independent” variable (y1). The relation is that given any set of observations on the relevant variables, we can calculate a constantk* and set of constantsb1*,ci*,hb1, andhci(i= 1, …, λ) such that any estimated coefficientsb1andciare related to the value ofkcorresponding to the estimating procedure by rectangular hyperbolas