One thing to consider if you are monitoring your BP is when and under what conditions you take it. When I sit down to take it the first reading may or may not reflect my at rest BP. If I have been moving around a lot or been active it might be a little higher. Then if I relax, feet flat on the floor sitting down, by elbow about the height of my heart it will come down. I usually take it three times in a row. Sometimes all three readings will be not much different. Sometimes the second or third will be quite a bit lower than the first.
The important thing, in my opinion, is that a person is relaxed. Blood pressure is supposed to raise during stress or exercise. As the body requires more energy the heart responds and increases heart rate and thus the associated pressure pushing the blood through the vascular system. So in my opinion if a person checks his blood pressure at a time when it is normal for blood pressure to be elevated, like right after exercise, he is going to have a higher reading.
Some people just the anxiety of a doctor office visit will cause temporary high blood pressure.
For that reason if a person has been told they have high blood pressure buying a GOOD quality BP machine and monitoring it themselves over a period of time when at rest will give a much better picture of any blood pressure issues.
Another thing to keep in mind is resting heart rate. Mine will sometimes be as low as 50. Makes a big difference on how hard your heart is working if it is beating 50 or 100 times a minute. Mine normally runs 50-65 when I check it, indicating to me it is not having to work very hard to supply blood to where it is needed. Heart rate will vary a lot between individuals.
There have been some really good videos that showed statistics of where the cutoff is where it is just as big of risk to take the BP medicines as the slightly high BP was causing risk. But I think the info was embedded in videos about low carb stuff and I can not locate them easily. But if I recall correctly I think it was 140/80 for older people. Below that the BP medicines that were being tested did not improve all cause mortality. Above that they had slightly decreased all cause mortality. In other words above 140/80 taking the medicine might help. Below that not likely. But that is going from memory which is often faulty so don't "take that to the bank" so to speak.