I too use the Omron BP monitor; works pretty good; but sometimes the cuff has to be snug enough for an accurate reading. My doctor also said to line up the tubing with your vein in your arm for accuracy.I also plug mine into the wall; batteries do not last that long in mine. Beginning to wonder about my diagnosis with BP. Quit taking my meds two weeks ago; and my blood pressure has been staying in the 120's. Meds was causing bad leg cramps and lightheadness.I'm talking leg cramps so bad that when you roll over in bed at night; I would get them. Hope that I am not damaging my heart my going on and off these different meds.
Not sure about this, but they do vary in quality and reliability of measurement. This may be a better question for the more tech savvy forum frequenters.
I also use an Omron, a wrist monitor that requires you to have it in the correct position or it won't take a reading. I also take mine to my doctor's office to check it's accuracy and it's always spot on.
Not to promote any device here but i have an an Omron took it to the hospital to compare and its accurate within 1-5 points or exactly the same can't get no better than that.