A harvester having: a harvester base cutter control system comprising: a first height sensor (215; 530; 625; 725) mounted in a row separator (120; 210; 510; 615; 715) of the harvester (105; 405; 505; 605; 705) to measure a height, h1, of a base cutter (130; 205; 515)/row separator (120; 210; 510; 615; 715) unit above a rut (125; 305; 420; 540; 635; 640; 650) traversed by tracks or wheels (115; 415; 520; 610) of the harvester (105; 405; 505; 605; 705); a second height sensor (410; 535; 630; 730) mounted at the rear of the harvester (105; 405; 505; 605; 705) to measure a height, h 2, of the harvester (105; 405; 505; 605; 705 above a furrow (135; 310; 425; 645) between the tracks or wheels (115; 415; 520; 610); a controller configured to interpret sensor data h1, h2; characterised by: a hydraulic system to raise or lower the base cutter/row separator unit with respect to the harvester; the controller being configured to adjust base cutter (130; 205; 515)/row separator (120; 210; 510; 615; 715) height via the hydraulic system to maintain a constant base cutter height above the furrow (135; 310; 425; 645); the controller comprising a pitch sensor configured to measure a pitch angle of the harvester (105; 405; 505; 605; 705); the controller being arranged to ignore changes in said height h2 when the pitch angle is changing or has been constant for less time than the harvester (105; 405; 505; 605; 705) takes to traverse a distance equal to a separation between the first (215; 530; 625; 725) and second (410; 535; 630; 730) sensors. a first height sensor (215; 530; 625; 725) mounted in a row separator (120; 210; 510; 615; 715) of the harvester (105; 405; 505; 605; 705) to measure a height, h1, of a base cutter (130; 205; 515)/row separator (120; 210; 510; 615; 715) unit above a rut (125; 305; 420; 540; 635; 640; 650) traversed by tracks or wheels (115; 415; 520; 610) of the harvester (105; 405; 505; 605; 705); a second height sensor (410; 535; 630; 730) mounted at the rear of the harvester (105; 405; 505; 605; 705) to measure a height, h 2, of the harvester (105; 405; 505; 605; 705 above a furrow (135; 310; 425; 645) between the tracks or wheels (115; 415; 520; 610); a controller configured to interpret sensor data h1, h2; characterised by: a hydraulic system to raise or lower the base cutter/row separator unit with respect to the harvester; the controller being configured to adjust base cutter (130; 205; 515)/row separator (120; 210; 510; 615; 715) height via the hydraulic system to maintain a constant base cutter height above the furrow (135; 310; 425; 645); the controller comprising a pitch sensor configured to measure a pitch angle of the harvester (105; 405; 505; 605; 705); the controller being arranged to ignore changes in said height h2 when the pitch angle is changing or has been constant for less time than the harvester (105; 405; 505; 605; 705) takes to traverse a distance equal to a separation between the first (215; 530; 625; 725) and second (410; 535; 630; 730) sensors. a hydraulic system to raise or lower the base cutter/row separator unit with respect to the harvester; the controller being configured to adjust base cutter (130; 205; 515)/row separator (120; 210; 510; 615; 715) height via the hydraulic system to maintain a constant base cutter height above the furrow (135; 310; 425; 645); the controller comprising a pitch sensor configured to measure a pitch angle of the harvester (105; 405; 505; 605; 705); the controller being arranged to ignore changes in said height h2 when the pitch angle is changing or has been constant for less time than the harvester (105; 405; 505; 605; 705) takes to traverse a distance equal to a separation between the first (215; 530; 625; 725) and second (410; 535; 630; 730) sensors.