Hi Maxwin, these portable machines are a bit inaccurate but there's a way to decrease error by taking 3 consecutive measurements and considering the average reading. Some machines automatically calculate the average of the last 50 or more readings. Which one is yours? I take 3 consecutive readings in the morning, 3 in the evening and 3 at night before going to bed, in a total of 9 readings a day. My machine stores 50 readings and gives me the average reading, which currently is 128/80, pulse 81, although I have some very high readings(167/100) and some low ones (97/65), but the average reading is pretty good.