When I went to the medical exams to get my drivingllicense one year ago I was told my blood pressure was a bit high - maybe due to the nervousness of being checked, but it was better to ask my doctor - both of my parents suffer from high blood pressure.
So I did. He told me my blood pressure was high and gave me that famous table to fill up with daily readings for two weeks.
My sister (physiotherapist) has a sphygmomanometer at home but she will scream at me to be perfectly still and seated for at least 5 minutes before doing the reading - and it _always_ was 120/80.
Went several days to a nearby pharmacy and they gave me a little chair to be sat for 10 minutes before standing up and going to a small cubicle where they did the measurement with an electronic sphygmomanometer. Measurements there always were fairly inconsistent and above 131/87 - going up to 150/87.
Also went to several other points to get my blood pressure measured and they always had a different method and (unsurprisingly) yielded different results. But for some reason when they measured with analogic/traditional sphygmomanometers, the measurements always were lower compared with electronic ones.
Fortunately could afford a decent electronic sphygmomanometer for myself and started doing my own measurements, which are fluctuating between 117/77 and 122/82.