Common types of variometers include those based on a diaphragm, a vane (horn), a taut band, or are electric based. The vane variometer consists of a rotating vane, centered by a coil spring, dividing a chamber into two parts, one connected to a static port, and the other to an expansion chamber. Electric variometers use thermistors sensitive to airflow, or circuit boards consisting of variable resistors connected to the membrane of a tiny vacuum cavity.[5][6][7][8]