What kind of monitor you are using for measurement?
Are you relaxed while taking your blood pressure?

Yeah its a electric monitor with the right sized cuff etc, sitting in the same position each time relaxed etc.

To ensure consistency in your blood pressure readings, you should take your blood pressure at the same arm, at the same time everyday, in the mornings or at bed time.
Do not take coffee or cigarettes for at least 30 minutes before taking your reading.
Also, remember that an average of two different readings taken at least 5 minutes apart is more reliable than 1 reading.