Medical fact;
When doctors measure blood pressure for the first time in a patient they should check both arms, as the readings may differ significantly.
This guideline isn’t followed everywhere. For example,
one case where a patient was being taken on and off his medication every couple of months simply because every time he visited the doctor, the reading was taken from a different arm.

Blood pressure also changes very quickly when taken on the same arm.  I once took a patient’s blood pressure when they first entered the exam room and charted the reading; the doctor walked in 1/2 hour later and took the patient’s blood pressure again, the reading was different.  This same doctor came out of the room and proceeds to tell me off, questioning my skills as a nurse.  I bit my tongue and thought you idiot blood pressures changes quickly.  You had that patient sitting in your exam room for 1/2 hour waiting.  What the bleep do you expect?  Now I think back on it 1/2-hour wait was not all that bad, at late when I go into to see the doctor I wait for 1 hour or more.