This read-write object configures the impedance -- 75, 100, or 120 ohms -- expected on the external clock input of the AUM card. It must match the impedance of the actual external timing source's cabling and connector standard for the clock signal to be interpreted correctly. An admin connecting a BITS (Building Integrated Timing Supply) reference with a 120-ohm balanced interface would set this object to ohms120 to match, rather than leaving it at a mismatched value that could cause clock recovery errors.