Interesting. You might want to factor in the blood pressure level where high blood pressure is supposed to start. My blood pressure has been the same for most of my life, but, a few years ago the pressure level where high blood pressure is supposed to start was LOWERED and now I am considered to have high BP.

Blood pressure readings in doctor's offices and hospitals are usually on the high side because most people are nervous and/or in pain when they are there, automatically raising their blood pressure.

I got a home blood pressure monitor since my husband won't see a doctor unless he's dying, and I rarely go myself, but we are in our 50s and it is important to keep tabs on it. Particularly for hubby, since he day trades stocks for a living and I know he gets worked up every day over the way the stock market is manipulated.

Sure enough, several readings at different times of day while he was relaxed show that he now is in the hypertensive range (over 135 systolic).

I'm not sure how correctly calibrated the home machine is, so I will watch for changes in the numbers rather than the actual numbers themselves.

Actually, a couple of mm really isn't that much. And isn't that likely to get you placed on meds. A bigger issue is the person taking the pressure using the wrong cuff size. Someone with big arms needs a larger cuff. And I don't just mean fat arms. Also muscular. A cuff that is too small will give a much higher reading...sometimes 15-20mm/mg than one which is the correct size.
Conversely, a cuff which is too large for the patient, can show a much lower pressure than they really have.

Finally, watch the person taking your pressure. If they deflate the cuff too fast, there is NO WAY they will get an accurate reading. This type of reading could be off only a small amount or a much larger amount; basically depending on the current heart rate of the patient. The faster the deflation especially with a slow heart rate the more inaccurate the reading.

Now, to clarify my above statement....having only a couple of mm/mg off of calibration is bad, because in my medical opinion, it shows a lack of attention to detail by the provider. Especially since calibrating it takes only a few seconds......

Hypertension can't be diagnosed until you have three BP readings (all 1-2 weeks apart) of systolic over 139 or diastolic over 89. If you think the cuff is poorly calibrated, check your blood pressure every time you go to a grocery store (most have free automated cuffs at the pharmacy) or buy a home monitor (plenty under $20 now) and keep a personal log to take to your doctor.

Blood pressure readings can vary throughout the day.I know this because I became alarmed when my blood pressure escalated from the stress of my nursing program. So now I frequently monitor myself and have both a manual and automatic cuff, and to check accuracy of either, I have compared readings and they usually are within a couple of points of each other. So personally, I feel the automatic cuffs are just as accurate as manual. But to respond to your OP, my BP will go up and down throughout the day so variations are not unusual. Causes of the variations can be responses to stress, diet, fluid balance. Constant elevation can indicate atherosclerosis and cholesterol deposits. A cholesterol screening would be a good place to start if consistently high.