With "Cap enable" selected on EEG Cap tab in Neurobit Optima+ settings, "Common reference" will switch "Internal connection" and be inactive. Ear clips connected to the caps drop wires are automatically linked and cannot be unlinked. To allow independent references, do the following:
1) Connect long tin ear clip electrodes to the ear lobes and to the Optima's A- and B- connection ports.
2) Load from Documents\Neurobit the settings file EEG 4C (I) Independent.nbc