Reliability of blood pressure machines.

I was put on a 24 hour blood pressure machine once. It registered normalish levels. It's always high when it's measured at the docs.

I am pretty sure that the one I was wearing was dodgy. The cuff slipped a lot and it never seemed to get very tight.

I take my FIL’s blood pressure fairly regularly using my sphyg and stethoscope to avoid him having to go to the surgery. They seem happy with that. I do avoid him trying to get me to use his WW1 BP set given to him my the GP who sold him his practice although I hope he leaves it to me when he eventually shuffles off this mortal coil.

I always insist on the GP using the 'old fashioned' one - as, in my case, it predictably returns a lower reading. There's quite a difference.

It's not down to either being faulty, though. I think my BP just shoots up when I anticipate my arm being squeezed too tightly.

One day, I got a cab there, instead of dashing up the hill from the station, as usual. The doctor said 'I can't believe it - your BP's normal!'

BP is measured in mm of Mercury (Hg). So the only absolute measurement is with a mercury in glass phygmomanometer
The electronic and dial gauge ones are pressure gauges which should be calibrated against a Mercury column.
We use an Omron, because that seems to be the one most used by the medical profession. The instructions advise regular calibration.
They can be inaccurate, if not checked and adjusted regularly.
In industry, instruments are checked at regular intervals, to ensure that they are accurate.
Readings at the surgery are likely to be higher because of "White coat syndrome", the tension of being under scrutiny at the surgery, probably plus the stress of getting there.

128/82 mmHg is in the normal range for women over 60. Seems pretty good to me, and your high BP is being managed well.
Before I retired I was senior nurse in nursing home. We used the Omron BP machines. I found them to be very accurate.

I bought the Omron our surgery nurse suggested we check both arms. It is very reliable my husband had his medication changed and he felt unwell.we monitored his bp and informed the surgery. He was then taken off the new medication and his bp was improved.

I have been taking my own BP every morning before I have my breakfast after having my tablets for 4 years. I use one made by Braun. Never it's different every morning. If it was the same then the machine is faulty. If I have had a bad night my BP is always higher than if I had a full night's sleep. My BP is always higher when I have it done at the hospital or GPs. Mainly because it's later in the day and I have been active .

Taking my BP every day I know what my usual range is. So if it's shots up for a couple of days I know something is wrong . Usually I have a virus or infection.

I didn’t realise that BP goes up and down all day and night till I had a 24hr monitor fitted. This explained why my BP readings were changing through the day. Agree that the old fashioned sphygmomanometer is more accurate and used by cardiologists to get an accurate reading.

My surgery accepts my twice a day for 7 days home readings once a year, they also advise average of three readings each time. I buy a new machine about every three years..

Those home ones are iffy.
If you do use one do x3 with about 2 mins gap between then mean the results. Use that as your home BP.
If it's done by a Sphyg and stethoscope you will be lower as you hear better, the cut in and off point better.

In my experience achieving two similar readings in a row is unlikely. It's not the meter that varies, it's you. Mine has been marginal for donkey's years and mostly it's white coat syndrome and as BlueBelle says, it's easy to get would up even when testing yourself. After I kept returning marginal figures (upper end of normal is 140/90) and I got cheesed off with the health Stasi chasing me for readings all the time I asked for a 24h monitored measurement. The figures must have been fine because I didn't hear again for a couple of years! The two devices I have - both Omron - return similar figures although one was about £100 in 1998 and the other about £35 a year ago. Go for the best of three was the advice I was given.

Whenever I have my bp taken at a doctors or hospital etc it is up up and the doctor / nurses always recognise that it’s white coat syndrome although I never feel the least bit ruffled or anxious
When I first bought my machine it was up because I was thinking ‘am I doing this right’ ‘will it stop squeezing’ Once I was used to taking it it was normal and I took it twice a day for two weeks with it staying normal and sent the reading off to my gp and he was satisfied
I can’t comment on any different machines but the gp didn’t suggest I bought anything special just told me to get one of the shelf or Amazon so I wouldn’t think there’s much difference or else they would advise a certain type
I haven’t used it since