Update. After sending this back to Omron for testing, I've been assured from their techs that the unit is fine. That a unit that they say checks out gives me blood pressure readings that are about as good as random as the lottery gives me pause in recommending this method of testing blood pressure.
Phone support did provide a few helpful hints that somewhat reduced the errors. One (not shown in the manual) is to always rest the arm you're taking the measurement from on a table. They said that the measurement method is highly sensitive to vibrations and movement and the table helps reduce those errors. I might give that idea another chance. I'm not hopeful that it will work for me. I wish future purchasers all the luck in the world to get it to work for them.
Prior review: I think I got a lemon. Consumer Reports lists this model as top choice. Mine gives me readings that are seldom anywhere near what my doctor gets. Even when we run them side by side. I hope I can figure out how to do a return and replacement.