The (Ground)-Splitter is used to connect two ground cables to one and the same NeXus. With this cable you could connect two people to one NeXus for doing two persons EMG/ECG/EOG/EEG
Please note that by splitting the ground the noise level on your signal will increase. If you use peripheral (AUX) sensors, you can connect as many people as there are AUX channels available, e.g. 4 respiration in NeXus-10.