Target Heart Rate ?

[Panzerfaust]

I would also invest in a HR monitor, i got mine at wal-mart and like said above you wear it around your chest and you have a watch that comes with it.

[ducatibob]

Invest in the heart rate monitor. Most of the equipment at your average gym has "Polar Link” the telemetry that links the watch to the chest strap also links to the machine. You can pick the "heart rate" program and set the heart rate you want. The machine then usually gives you a 5-minute warm up and then adjusts the resistance or incline until you reach your target. As the workout goes on the machine continually adjusts to you.

This allows you to optimize your cardio time. It's also a great way to circuit train, 2 minutes at 85% MHR / 3 minutes at 65%.

Plus it's a great way to track your cardio vascular progress. A lot of people start out at 30 minutes 4 mph, 2% incline etc. After a few weeks your body has adapted, but people keep doing the same routine.