In general, the higher blood pressure arm is the more accurate blood pressure. Keep in mind that most home blood pressure monitors are made to utilize the left arm. You'll note a little picture on the cuff demonstrating how the cuff should be positioned. On the left arm the tube coming out of the cuff should generally run down the center of the underside of your arm. There is usually a marked area with a red or green stripe which then is positioned over the inner half of the underside of your arm which is where the artery running down the arm is positioned and where the device should be "listening". that's the same area where your doctor places a stethoscope when he uses a sphygmomanometer in the office. I've never dismantled a blood pressure cuff but if you utilize your cuff on the right arm it's probably best to have that marked area positioned on the inside half of the underside of your right arm. if you press that area firmly with your fingers you'll feel the pulse of your brachial artery.
As you probably have already discovered, blood pressures run in a range.
you generally want the top number running 130 or less and the bottom number 80 or less. As someone mentioned before it's a good idea to bring your blood pressure monitor into your Dr. or NP's office to have it compared to the sphygmomanometer used in the office. In general arm cuffs are spot on or a run a bit high. wrist blood pressure cuffs tend to be inaccurate and probably should be avoided.