A method and tool for comparing mammals, such as horses, the tool including an electrode an electronic heartbeat measurement instrument an analyzer for determining an output indicative of adaptability, reactivity, or equanimity and a plotting system for plotting the temperament parameter or temperament quotient on a grid. The tool is used to provide a value for the sympathetic nervous system index (SNSI), the parasympathetic nervous system index (PNSI), or the standard deviation of average mode normal to normal intervals (SDMNN). This value is correlated to a selected characteristic of the mammal.
