​If you’ve been checking up on your blood pressure from home, it’s more than likely you’ve gotten skewed results.

Home blood pressure monitors are wrong more often than not, according to a new study in the American Journal of Hypertension.

University of Alberta researchers compared 85 people’s at-home BP monitor results to measurements taken by two separate people with a mercury sphygmomanometer—a more reliable method known as the gold standard for accurate readings.

The at-home monitor results were off the mark by at least 5 millimeters of mercury (mmHg) 69 percent of the time. And 29 percent of the time, they weren’t even within 10 mmHg.

Men, older people, and those with larger arm circumferences were more likely to get inaccurate results, and devices with hard cuffs were more likely to produce them.

These factors can give you a skewed reading because a poor fit can alter pulse pressure or make your veins stiffer, the researchers explain.

High blood pressure is the world’s biggest source of death and disability, and accurate measurements are necessary for either initiating treatment or tweaking it accordingly.

So it’s important not to rely on skewed readings, lead author Jennifer Ringrose, M.D., said in a press release.

If you use a BP monitor, she suggests comparing its readings the doctor’s so you know how off it is. And don’t base any medical decisions off just a few readings.

For instance, Canadian guidelines—where the study took place—recommend at least 28 at-home readings per week.

"What's really important is to do several blood pressure measurements and base treatment decisions on multiple readings,” she said in the release.

“Taking home readings empowers patients and is helpful for clinicians to have a bigger picture rather than just one snapshot in time."

In the meantime, make the most out of your at-home blood pressure measurements with these tips.

First, choose an upper-arm monitor over a wrist one, which tend to be less accurate, says Brent Egan, M.D., a hypertension researcher at the Medical University of South Carolina.

Try one that has been vetted by the Dabl Educational Trust and the European Society of Hypertension—check out the list at dableducational.org.

Then, when it’s time to take your reading, sit with your feet on the floor and straighten your back with arms supported at heart level.

Give yourself five minutes to rest quietly before slapping on the cuff. This will help make sure you are getting a true reading, he says.

Additional reporting by Christa Sgobba