My college helping me set up for the experiment I just did. This is how we add gel to the head, there is a tiny hole by each sensor, we then insert a blunt tip needle (we do NOT puncture the skin!) to add the gel between the sensor and the top of the head to eliminate the air gap caused by the hair. Unfortunately it looks scary, but we need something tiny to get around the sensor (if you look close you can seethe tiny, tiny opening each senor has). The lights on each sensor tell us how good of a connection we have, red means bad, yellow means we’re getting close, and green means good.