A computer-assisted medical system (100, 200) comprising: a computer-assisted medical device (110, 210, 420, 1101, 1111, 1121, 1131, 1141, 1151, 1161) comprising an articulated arm, the articulated arm configured to have a distally mounted instrument (270, 1105, 1142), wherein the distally mounted instrument (270, 1105, 1142) is configured to be inserted at a body opening into a patient on a surgical table; and a control unit coupled to the articulated arm; wherein the control unit is configured to: determine a first motion of the surgical table (170, 280, 410, 1100) based on information received from the surgical table (170, 280, 410, 1100), the surgical table (170, 280, 410, 1100) being coupled to the control unit via a communications connection, the first motion of the surgical table (170, 280, 410, 1100) causing a corresponding second motion of a control point of the articulated arm due to movement of a portion of an anatomy of the patient, the portion of the anatomy corresponding to the control point when the instrument is inserted at the body opening; characterized in that the control unit is further configured to: determine a first angular direction of a horizontal component of the first motion relative to an axis in a surgical table coordinate frame; determine a second angular direction of the second motion relative to an axis in a computer-assisted medical device coordinate frame; and determine a third angular relationship between the surgical table coordinate frame and the computer-assisted medical device coordinate frame based on a difference between the first and second angular directions. a computer-assisted medical device (110, 210, 420, 1101, 1111, 1121, 1131, 1141, 1151, 1161) comprising an articulated arm, the articulated arm configured to have a distally mounted instrument (270, 1105, 1142), wherein the distally mounted instrument (270, 1105, 1142) is configured to be inserted at a body opening into a patient on a surgical table; and a control unit coupled to the articulated arm; wherein the control unit is configured to: determine a first motion of the surgical table (170, 280, 410, 1100) based on information received from the surgical table (170, 280, 410, 1100), the surgical table (170, 280, 410, 1100) being coupled to the control unit via a communications connection, the first motion of the surgical table (170, 280, 410, 1100) causing a corresponding second motion of a control point of the articulated arm due to movement of a portion of an anatomy of the patient, the portion of the anatomy corresponding to the control point when the instrument is inserted at the body opening; characterized in that the control unit is further configured to: determine a first angular direction of a horizontal component of the first motion relative to an axis in a surgical table coordinate frame; determine a second angular direction of the second motion relative to an axis in a computer-assisted medical device coordinate frame; and determine a third angular relationship between the surgical table coordinate frame and the computer-assisted medical device coordinate frame based on a difference between the first and second angular directions. determine a first angular direction of a horizontal component of the first motion relative to an axis in a surgical table coordinate frame; determine a second angular direction of the second motion relative to an axis in a computer-assisted medical device coordinate frame; and determine a third angular relationship between the surgical table coordinate frame and the computer-assisted medical device coordinate frame based on a difference between the first and second angular directions.