The welding robot on the body-in-white line pauses mid-stroke, its arm hovering above the door sill. A small rotary sensor mounted on the joint shaft tracks the exact angle of the wrist, sending real-time position feedback to the controller. Every fraction of a degree adjusts the torch path, ensuring the weld seam follows the programmed curve without deviation. If the sensor drifts or fails, the robot either skips the weld or burns through the panel—both costly rework scenarios. Downstream, the same sensor type monitors the tilt of the adhesive dispensing head, guaranteeing a consistent bead width before the roof panel is bonded. In final assembly, a linear version measures the stroke of the seat-height adjuster motor, confirming the seat has reached the correct position before the bolt is torqued. Each sensor operates in a sealed housing, protected from welding sparks, paint overspray, and the constant vibration of the line, yet remains accessible for quick replacement during scheduled maintenance windows.