I’m a proponent of my patients monitoring their blood pressure at home. However, there are a couple of concerns when using a home monitoring device to measure blood pressure:

• which arm to use, and
• how long to wait before testing.

Recently, the Mayo Clinic and the American Heart Association have some guidance on the subject.
There’s usually a slightly measurable difference in blood pressure between your arms, according to the heart association. Your dominant arm will probably be higher. If you’re left-handed, pressure may be higher in the left arm, and vice versa.
It shouldn’t make a huge difference, but, the association adds: “If one arm has higher blood pressure than the other, that arm should be used to determine if you have hypertension.”
Note: If the difference in readings between your left and right arms tops more than 10 mm Hg (millimeters of mercury), there could be other underlying problems that should be checked out with your doctor.
As for how long to rest before taking your blood pressure, the Mayo Clinic suggests three to five minutes; the Cleveland Clinic suggests five to 10. Essentially, all you need is enough time to sit quietly and relax.
Finally, here’s a handy video from the Mayo Clinic on how to measure your blood pressure using an automatic monitor.