A system comprising: a power wrench; and a controller operatively connected to the power wrench, wherein the controller is configured to perform actions including: directing (P1, P2, P3) an operative head of the power wrench to turn in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, defining an origin at an angular position of the operative head where the pressure-angle derivative of the operative head exceeds the predetermined threshold, directing the operative head to turn by an angular step in response to: (a) the pressure-angle derivative of the operative head exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the angular differential represents a total amount of rotation of the operative head from the origin; and directing the operative head to cease turning in response to the angular differential of the operative head being approximately equal to or greater than the target value, characterised in that the controller is further configured to perform actions including: determining whether the pressure against the operative head is outside a tolerance band in response to the angular differential being approximately equal to or greater than the target value, and directing the operative head to turn by an angular correction in response to the pressure against the operative head being outside the tolerance band (P8, P9). a power wrench; and a controller operatively connected to the power wrench, wherein the controller is configured to perform actions including: directing (P1, P2, P3) an operative head of the power wrench to turn in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, defining an origin at an angular position of the operative head where the pressure-angle derivative of the operative head exceeds the predetermined threshold, directing the operative head to turn by an angular step in response to: (a) the pressure-angle derivative of the operative head exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the angular differential represents a total amount of rotation of the operative head from the origin; and directing the operative head to cease turning in response to the angular differential of the operative head being approximately equal to or greater than the target value, characterised in that the controller is further configured to perform actions including: directing (P1, P2, P3) an operative head of the power wrench to turn in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, defining an origin at an angular position of the operative head where the pressure-angle derivative of the operative head exceeds the predetermined threshold, directing the operative head to turn by an angular step in response to: (a) the pressure-angle derivative of the operative head exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the angular differential represents a total amount of rotation of the operative head from the origin; and directing the operative head to cease turning in response to the angular differential of the operative head being approximately equal to or greater than the target value, characterised in that the controller is further configured to perform actions including: determining whether the pressure against the operative head is outside a tolerance band in response to the angular differential being approximately equal to or greater than the target value, and directing the operative head to turn by an angular correction in response to the pressure against the operative head being outside the tolerance band (P8, P9).