Pre-set the monitor for a work time of 12:00 and a rest time of 4:00. Let your cadence vary as follows per interval: First interval: 5 minutes @ 75 rpm, 1 minute @ 85 rpm, 5 minutes @ 75 rpm, 1 minute @ 85 rpm. Second interval: 4 minutes @ 75 rpm, 2 minutes @ 85 rpm, 4 minutes @ 75 rpm, 2 minutes @ 85 rpm. Third interval: 3 minutes @ 75 rpm, 3 minutes @ 85 rpm, 3 minutes @ 75 rpm, 3 minutes @ 85 rpm. Fourth interval: 2 minutes @ 75 rpm, 4 minutes @ 85 rpm, 2 minutes @ 75 rpm, 4 minutes @ 85 rpm. During the rest time continue rowing at light pressure.