A method of using array calorimeters, comprising: for each of a set of two or more cells of an array calorimeter: providing respective test and reference groups of samples, wherein each sample consists of droplets of equal size; the test group including at least a respective first sample that includes molecules of one or more target types and a respective second sample that includes fragments of one or more fragment types, each of the first and second samples not exceeding 100 microliters; the reference group including respective first and second samples similar to the test group's first and second samples; combining at least the first and second samples of the cell's test and reference groups; and providing respective output signals that include information about heat of reaction due to combining the first and second samples of the cell's test group; characterised in that for each of a set of one or more of the target types, the output signals are used to rank fragment types that react with the target type; wherein the act of using the out put signals to rank fragment types includes obtaining a rank ordering of a subset of the fragment types that react measurably with the target type, the rank ordering depending on ligand efficiencies of the fragment types. for each of a set of two or more cells of an array calorimeter: providing respective test and reference groups of samples, wherein each sample consists of droplets of equal size; the test group including at least a respective first sample that includes molecules of one or more target types and a respective second sample that includes fragments of one or more fragment types, each of the first and second samples not exceeding 100 microliters; the reference group including respective first and second samples similar to the test group's first and second samples; combining at least the first and second samples of the cell's test and reference groups; and providing respective output signals that include information about heat of reaction due to combining the first and second samples of the cell's test group; characterised in that for each of a set of one or more of the target types, the output signals are used to rank fragment types that react with the target type; providing respective test and reference groups of samples, wherein each sample consists of droplets of equal size; the test group including at least a respective first sample that includes molecules of one or more target types and a respective second sample that includes fragments of one or more fragment types, each of the first and second samples not exceeding 100 microliters; the reference group including respective first and second samples similar to the test group's first and second samples; combining at least the first and second samples of the cell's test and reference groups; and providing respective output signals that include information about heat of reaction due to combining the first and second samples of the cell's test group; characterised in that for each of a set of one or more of the target types, the output signals are used to rank fragment types that react with the target type; wherein the act of using the out put signals to rank fragment types includes obtaining a rank ordering of a subset of the fragment types that react measurably with the target type, the rank ordering depending on ligand efficiencies of the fragment types. obtaining a rank ordering of a subset of the fragment types that react measurably with the target type, the rank ordering depending on ligand efficiencies of the fragment types.