At my age, it is prudent to check blood pressure. I've been doing this for some time, with an electronic BPM (Blood Pressure Monitor), which we've had for years. The Velcro, which holds the pressure cuff to your arm, is worn, so I decided to check the latest models on Consumer Reports website. This organization is not sponsored by any other organization; it tests consumer products by buying them as you and I would. Any major purchases we intend to make are first vetted by us here. So, when I looked for test results for BPMs, I found the top model. I went to our mall and looked for it, found the shelf on which it was supposed to sit at a pharmacy there. The shelf had the label of the correct model, but the BPM sitting there was a different model, by the same manufacturer. Since the people at the pharmacy did not have the model I wanted in stock, I decided to take the model I found.
Starting with this new BPM, I found that my blood pressure readings seemed to be about 20mmHg (20 mm of mercury) higher than on my old unit. This certainly caused me some concern. At that point I didn't know whether the old BPM had given me incorrect readings all along, or whether the new one was incorrect. This discrepancy persisted, so I made an appointment with our doctor. The intent was to compare the new machine with the doctor's BPM. Well, the result was that the new BPM read about 20 mmHg higher than the doctor's, too.
So, my advice, if you are doing something similar, go to your doctor and make sure the readings on your BPM matches the ones on his/hers to within a couple of points, or so. Take your BPM along with you, so you can compare them. Both you and your doctor may be making medication decisions based on the readings you are taking at home (to avoid the "white coat" syndrome). If these decisions are based on incorrect readings, the medical consequenses might be more serious than a blood pressure problem itself.