Many bicycles will not shift or track properly because the front and rear wheels are not in line with the frame. If these conditions still exist after wheel and derailleur adjustments, the seat stays, chain stays, and rear drop outs of the frame may be misaligned. For years the accepted method to check the alignment of the rear drop-out was to run a string on either side. This method does work to some extent. However, it is not accurate because the measurement is not taken at the drop-out. With the Park Tool Frame Alignment Gauge the alignment can be checked quickly and accurately at the drop-out. Retractable pointer to fit all sizes and types of bicycles.