Here is a list of some additional features commonly found on an advanced heart rate monitor (on top of basic and intermediate features):
Fitness Test
Personalised Fitness Training Program
Relaxation Measurement
Data Transfer to Web Site or PC for Analysis
Protection against Cross Talk Interference
Speed and Distance Measurements
Fitness Test
Your can have your cardiovascular fitness tested on some advanced heart rate monitors (e.g. Polar F11). This feature is known as OwnIndex on Polar monitors. The end result can be comparable to a VO2 Max measurement. If you do this fitness test periodically, you will be able to see if your training has resulted in an overall improvement of your fitness over time. This feature is good for keeping up your motivation and measuring your progress.
Personalised Fitness Training Program
This feature is a very useful one, particularly if you have not worked out a structured training plan. Some monitors (e.g. Polar F11) can help you customize a personal training program, on a session-by-session basis, on what you need to achieve in terms of duration, calorific consumption and intensity of your workout. The customization will take into account your current fitness and your training goal. This is probably as close as you are going to get to having your own personal trainer.
Relaxation Measurement
This feature measures how you relaxed you are. You can do it in the morning, before or after an exercise. The more relaxed you are the better the measurement will be. This feature is available on some high end Polar monitors (e.g. Polar F55).
Data Transfer to Web Site or PC for Analysis
Some monitors support the transfer of the training data stored on your wrist watch to either a web site or a PC for further analysis. Make sure you know it is to which one, though, as they are quite different. If the transfer is to a web site, your data is stored on the web server, not locally on your computer. In that case you will also need an internet connection to access your data and to do the analysis. However, it is more common to download data to a computer and use PC software for analysis. Furthermore you may also find yourself needing a microphone or a speaker to do data transfer between your computer and your heart rate monitor wrist watch (e.g. many Polar models). So check the manufacturer's specification carefully.
Protection against Cross Talk Interference
Some high end fitness heart rate monitors come with coded wireless analogue transmission from the chest strap to the wrist watch. Compared to non-coded wireless analogue transmission, this feature offers enhanced protection from cross talk interference i.e. you are less likely to have your monitor readings disturbed by other users of heart rate monitors exercising nearby. A few heart rate monitors come with digital transmission. With these monitors, the chances of a cross talk interference are minimal but they can't interface with gym equipment such as treadmills.
Speed and Distance Measurements
Measuring speed and distance for runners usually require a separate foot pod to be worn. The foot pod then transmits speed and distance information to the wrist unit to be displayed real time while you are running. This is very useful information as it allows you to correlate your input (heart rate as a measure of your intensity) with your output (speed or pace). There are also heart rate monitor systems that use GPS for speed and distance measurements.