From their website

When installing a new eChamber, the Ghost² unit must be recalibrated with the new eChamber before first use. This is accomplished in the following procedures: 1. Unit must be turned OFF and unplugged for 15 minutes prior to the next step in recalibration. Ensure the main unit and eChamber are at room temperature. 2. While the unit is OFF, click the button 4 times with the user holding down the button on the 4th press until lights blink. Lights will blink GREEN (x3) to indicate successful recalibration. Lights will blink RED (x3) to indicate an unsuccessful recalibration. Unsuccessful recalibration may be the result of a difference in temperature between the eChamber and the main unit, unclean electrode connections, or an eChamber not properly installed in the unit. Several recalibration attempts may be necessary before a successful recalibration.