It's called the silent killer because there are no signs and symptoms of high blood pressure, so getting an accurate reading the right way is very important.

Now more than ever, doctors realize your blood pressure number is important. The top should be less than 120 and the bottom less than 80. A recent study showed when your numbers are even a little higher, like the top in the 130s and the bottom in the 80s, it's dangerous.

"When you're in that blood pressure range, on average you already have a doubling of heart attack risk and stroke risk," explained Tulane Epidemiologist, Internist, and Nephrologist Dr. Paul Whelton.

He is lead author of the new comprehensive clinical guidelines for blood pressure management published in the American Heart Association journal Hypertension and the Journal of the American College of Cardiology. (He is also Show Chwan professor of global public health at Tulane University School of Public Health and Tropical Medicine.)

The study now better pinpoints guidelines and who needs high blood pressure medicine. Of course, the main way to combat this silent killer is diet and exercise, but how do you know if you're getting your real numbers in the doctors office?

"We stress the importance of accurate readings. We know that blood pressure is something that varies a lot."

Dr. Whelton says make sure the right cuff size is used on the top of your bare arm at heart level. Relax. Don't talk for five minutes. Keep both feet flat on the floor while sitting upright with your back straight in a chair. Make sure you've emptied your bladder and not had caffeine, nicotine or exercised 30 minutes before.

Some doctors say the manual cuffs are more accurate than the machine cuffs that are in 80 percent of medical offices. Patients even blog about the variation in their own numbers, but Dr. Whelton believes studies show machines are reliable, but need to be calibrated by the manufacturer once a year to assure accuracy.

He also says taking an average of home pressure readings is important because in 30 to 50 percent of the time, the reading may be a false low or false high in the doctor's office, throwing off the need for important treatments.

"Increasingly, we have learned that what we get in the office, is a small window and doesn't necessarily give us all the information and risk," he said.

But are those drug store machines and even those smart phone apps that take a picture of your finger reliable and accurate? In part 2, we do an experiment with our viewers to test store machines, and we'll tell you how you can get heart and blood pressure medicine for free, or for only $2.