Hypertension or raised BP is diagnosed by BP charting. BP has to be monitored daily at the same time for atleast 7 days. Preferably by a physician on a manual BP apparatus. If it is more than 130/90 mm Hg on multiple occasions, medications need to be started. Digital apparatus is good for emergency or for monitoring in an hypertensive person already on medications. It has an error of +/- 20-30 mm Hg and hence isn't very reliable for diagnosis of Hypertension.

Hii mam, There is many causes for high BP so diagnosis of high BP is important and accordingly treatment is given. Blood pressure should be measured regularly if you have high blood pressure..you can measure it at doctor clinic or at home..it is not important to measure everyday unless you have very high blood pressure like above 160/100.. Digital BP machine can show error in reading sometime..best way to measure it in doctor clinic with manual method...