You would have to send one or both back to the manufacturer if you found them inacurate, check your documentation on your machines I believe they have a place that tests the machines and make adjustments.
I took my machine to the doctor's office and took my BP there. It's always higher there . Then in about 10 minutes I had them take my BP with their equipment and compared the two. It was close enough, according to the nurse, that my machine is considered accurate. I have an Omron as well, but it's an older one. Still working ok