A surgical instrument for coagulating and dissecting tissue, the surgical instrument comprising: a processor; an end effector at a distal end of the surgical instrument, the end effector configured to interact with tissue, the end effector comprising: a clamp arm comprising an electrode; an ultrasonic blade; an ultrasonic transducer acoustically coupled to the ultrasonic blade and configured to receive a drive signal from a generator to cause ultrasonic motion of the ultrasonic blade and deliver ultrasonic energy to the ultrasonic blade; wherein the processor is configured to: control delivery of RF energy to the electrode at an amplitude or ultrasonic energy to the ultrasonic blade at an amplitude; measure tissue impedance of tissue engaged with the surgical instrument; characterised in that the processor is further configured to modulate delivery of the RF energy or delivery of the ultrasonic energy based on the measured tissue impedance; and when the measured tissue impedance reaches a threshold impedance, either: cease delivery of the RF energy and switch or transition to delivering ultrasonic energy, or cease delivery of the ultrasonic energy and switch or transition to delivering RF energy. a processor; an end effector at a distal end of the surgical instrument, the end effector configured to interact with tissue, the end effector comprising: a clamp arm comprising an electrode; an ultrasonic blade; a clamp arm comprising an electrode; an ultrasonic blade; an ultrasonic transducer acoustically coupled to the ultrasonic blade and configured to receive a drive signal from a generator to cause ultrasonic motion of the ultrasonic blade and deliver ultrasonic energy to the ultrasonic blade; wherein the processor is configured to: control delivery of RF energy to the electrode at an amplitude or ultrasonic energy to the ultrasonic blade at an amplitude; measure tissue impedance of tissue engaged with the surgical instrument; characterised in that the processor is further configured to modulate delivery of the RF energy or delivery of the ultrasonic energy based on the measured tissue impedance; and when the measured tissue impedance reaches a threshold impedance, either: cease delivery of the RF energy and switch or transition to delivering ultrasonic energy, or cease delivery of the ultrasonic energy and switch or transition to delivering RF energy. control delivery of RF energy to the electrode at an amplitude or ultrasonic energy to the ultrasonic blade at an amplitude; measure tissue impedance of tissue engaged with the surgical instrument; characterised in that the processor is further configured to modulate delivery of the RF energy or delivery of the ultrasonic energy based on the measured tissue impedance; and when the measured tissue impedance reaches a threshold impedance, either: cease delivery of the RF energy and switch or transition to delivering ultrasonic energy, or cease delivery of the ultrasonic energy and switch or transition to delivering RF energy. cease delivery of the RF energy and switch or transition to delivering ultrasonic energy, or cease delivery of the ultrasonic energy and switch or transition to delivering RF energy.