When viewing the sighting 'glass' of the CMP sensor there are 3 marks; a short line (on the left), a long line (almost the full height of the glass in the middle) and an arrow pointing clockwise (on the right). You will also see a vane through the glass when you rotate the sensor's drive gear. You need to rotate the vane clockwise so that the back edge of it lines up with the long mark.
The long line is shown in red and the vane in green.