mu Cap is a software package (citeware) for economic experiments enabling experimenters to analyze emotional states of subjects using z-Tree and FaceReader (TM). mu Cap is able to create videos of subjects on client computers based on stimuli shown on screen and restrict recording material to relevant time frames. Another feature of mu Cap is the creation of time stamps in csv format at prespecified screens (or at prespecified points in time) during the experiment, measured on the client computer. The software makes it possible to import these markers into FaceReader (TM) easily. mu Cap is the first program that significantly simplifies the process of connecting z-Tree and FaceReader (TM) with the additional benefit of extremely high precision. This paper describes the usage, underlying principles as well as advantages and limitations of mu Cap. Furthermore, we give a brief outlook of how mu Cap can be beneficial in other contexts.