Our amplifiers can collect EEG data with a unipolar montage. If you're using our standard EEG cap layout, the reference electrode is located at the FCz location, and ground electrode at the Fpz.
Your data can be later re-referenced using different methods in processing tools (average reference, mastoids etc.)
If you're using Smartfones, check out their configuration in another article linked here.
PRO line amplifiers can have up to 8 additional references for a bipolar measurement. Usually they are used for measuring other ExG data (EOG, ECG, etc.) See our article on bipolar channels - How to use ExG electrodes.