A surgical instrument comprising: an end effector comprising: a ultrasonic blade configured to ultrasonically oscillate against tissue; and a clamp arm configured to pivot relative to the ultrasonic blade; an ultrasonic transducer acoustically coupled to the ultrasonic blade, the ultrasonic transducer configured to ultrasonically oscillate the ultrasonic blade in response to a drive signal from a generator , wherein the end effector is configured to receive electrosurgical energy from the generator to treat tissue based on the drive signal; and a control circuit coupled to the end effector, characterised in that the control circuit is configured to: determine one or more of a resonant frequency measure indicative of a thermally induced change in resonant frequency and an electrical continuity measure; calculate a weld focal point based on one or more of the resonant frequency measure and electrical continuity measure; control closure of the clamp arm to vary a pressure applied by the clamp arm to provide a threshold control pressure to the tissue loaded into the end effector , wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade and clamp arm at a point proximal to a proximal end of the tissue. an end effector comprising: a ultrasonic blade configured to ultrasonically oscillate against tissue; and a clamp arm configured to pivot relative to the ultrasonic blade; a ultrasonic blade configured to ultrasonically oscillate against tissue; and a clamp arm configured to pivot relative to the ultrasonic blade; an ultrasonic transducer acoustically coupled to the ultrasonic blade, the ultrasonic transducer configured to ultrasonically oscillate the ultrasonic blade in response to a drive signal from a generator , wherein the end effector is configured to receive electrosurgical energy from the generator to treat tissue based on the drive signal; and a control circuit coupled to the end effector, characterised in that the control circuit is configured to: determine one or more of a resonant frequency measure indicative of a thermally induced change in resonant frequency and an electrical continuity measure; calculate a weld focal point based on one or more of the resonant frequency measure and electrical continuity measure; control closure of the clamp arm to vary a pressure applied by the clamp arm to provide a threshold control pressure to the tissue loaded into the end effector , wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade and clamp arm at a point proximal to a proximal end of the tissue. determine one or more of a resonant frequency measure indicative of a thermally induced change in resonant frequency and an electrical continuity measure; calculate a weld focal point based on one or more of the resonant frequency measure and electrical continuity measure; control closure of the clamp arm to vary a pressure applied by the clamp arm to provide a threshold control pressure to the tissue loaded into the end effector , wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade and clamp arm at a point proximal to a proximal end of the tissue. <EOS>