The study also suggested that professional rescuers tended toward rates of compression which were actually much too high (sacrificing compression depth and possibly not allowing veinous blood flow to return to the heart prior to the next compression). Metronomes or songs to set proper pace (We were recently taught to use "Staying Alive", the study suggests "Row, row your boat") seem to be effective in maintaining a proper pace.
For folks with Android smartphones, there is a CPR Metronome application for timing chest compressions.