When I first got my Ariel C class a few weeks ago, the speedo and odometer worked fine. Then they went blank. Ariel support suggested checking that the magnetic button and pickup sensor on the frame were in alignment. But this was no help. Then I had one of those "I wonder if . . . " moments, and tried rotating the magnet 180 degrees on the spoke, and that was the solution. One end of the sending unit is magnetic, the other end is simply the screw-on cap that locks it in place. The magnetic end was aimed the wrong direction, and rotating it put it right.