A surgical instrument comprising: an end effector (203120, 203200, 203220, 203340) comprising: a ultrasonic blade (203026, 203126, 203206, 203226, 203346) configured to ultrasonically oscillate against tissue; and a clamp arm (203022, 203122, 203202, 203224, 203342) 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 (203026, 203126, 203206, 203226, 203346) in response to a drive signal from a generator, wherein the end effector (203120, 203200, 203220, 203340) 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 (203022, 203122, 203202, 203224, 203342) to vary a pressure applied by the clamp arm (203022, 203122, 203202, 203224, 203342) to provide a threshold control pressure to the tissue loaded into the end effector (203120, 203200, 203220, 203340), wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade (203026, 203126, 203206, 203226, 203346) and clamp arm (203022, 203122, 203202, 203224, 203342) at a point proximal to a proximal end of the tissue. an end effector (203120, 203200, 203220, 203340) comprising: a ultrasonic blade (203026, 203126, 203206, 203226, 203346) configured to ultrasonically oscillate against tissue; and a clamp arm (203022, 203122, 203202, 203224, 203342) configured to pivot relative to the ultrasonic blade; a ultrasonic blade (203026, 203126, 203206, 203226, 203346) configured to ultrasonically oscillate against tissue; and a clamp arm (203022, 203122, 203202, 203224, 203342) 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 (203026, 203126, 203206, 203226, 203346) in response to a drive signal from a generator, wherein the end effector (203120, 203200, 203220, 203340) 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 (203022, 203122, 203202, 203224, 203342) to vary a pressure applied by the clamp arm (203022, 203122, 203202, 203224, 203342) to provide a threshold control pressure to the tissue loaded into the end effector (203120, 203200, 203220, 203340), wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade (203026, 203126, 203206, 203226, 203346) and clamp arm (203022, 203122, 203202, 203224, 203342) 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 (203022, 203122, 203202, 203224, 203342) to vary a pressure applied by the clamp arm (203022, 203122, 203202, 203224, 203342) to provide a threshold control pressure to the tissue loaded into the end effector (203120, 203200, 203220, 203340), wherein the pressure is varied based on a corresponding weld focal point; and maintain a gap between the ultrasonic blade (203026, 203126, 203206, 203226, 203346) and clamp arm (203022, 203122, 203202, 203224, 203342) at a point proximal to a proximal end of the tissue.