When observers judge the amount of a reward they consider just for target recipients, they may treat male and female recipients, differently, and this gender-based double standard my itself differ by the observer's own gender. In this paper we develop a framework that enables quantitative assessment of multiple standards as well as of the mechanisms by which they operate. The framework also makes it possible to test for differences in multiple standards across different subsets of respondents; and it is applicable to questions of multiple standards in both justice judgments and allocation decisions. To illustrate the framework, we examine a special case of multiple standards--gender-based double standards--and we focus on judgments of just earnings, using data collected by Rossi's factorial survey method. We conduct two main sets of analyses, the first focusing on the double standard and the second on the mechanisms by which the double standard operates. In the first set we estimate the just gender wage gap, in the eyes of male and female observers separately, establishing the existence and direction of the just gender wage gap and quantifying the differential across male and female observers. In the second set we assess the mechanisms by which the double standards operate, separating and quantifying two mechanisms--double standards in the just base wage (i.e., the base wage regarded as just by the observer) and in the just rate of return to schooling (i.e., the rate of return to schooling regarded by the observer)--establishing their direction and testing whether the mechanisms differ by observer's gender.