I brought my Japan made omron which I forgot the model, JPN 500 or something, to the pharmacy and check on my blood pressure on the spot using both their device and mine. (Same arm for sure) Ended up the Omron's reading is very much lower as compared to their Rossmax. Rossmax reading is more accurate as I have always been somewhere around that reading.

As far as I measured mine using that omron I always get shocked to have such low blood pressure and even start taking some salt thinking to replenish whatever that is lacking.

My blood pressure has been stable and consistent. Ever since using that particular device I keep on being in fear of that low blood pressure whilst my husband thought his blood pressure is getting so much healthier.

So better double check with another device before relying on just one. +/-20 is a lot!