Blood pressure changes virtually every minute in the body and home blood pressure monitors are not very accurate, they are simply an indication. At cardiac rehab their portable monitor was always putting me at 180/95 but whenever my GP checked it using a stethascope it was 145/80. Quite a large difference. If you change your posture, cough, burp, speak, chew, move your arm or anything, your blood pressure will change. It is always being monitored by the body and being adjusted. It isn't like the body says "ok for the next 24 hours we will keep it at 140/70", every single minute there are adjustments being made. Even during sleep it changes all the time. I had a friend who kept monitoring his blood pressure every few hours and taking his heart rate. It became an obsession to him and if it fluctuated slightly he was on the phone to his GP. Checking it once a week is adequate if you are not hospitalised, and even that's too often in my books.