Why does my automatic wrist blood pressure monitor say an unusually high number like 156/97 but my automatic digital monitor says 118/72? which is more accurate of the two, besides manual which is most accurate?

Likely, your wrist is not at the heart level when blood pressure is checked. The cuff on the upper arm is always at the heart level. Blood pressure is high at the wrist if it is below the heart level due to gravity + you blood pressure. In case your wrist is at the heart level when you have your blood pressure checked, I still believe the result from a conventional (upper arm) manometer.