In $ECG$,$P$-wave represents

Given below are two statements.
Statement $I$ - Graphical recording of electrical variations detected at the surface of body during their propagation through the wall of heart is electrocardiograph.
Statement $II$ - The instrument used for the graphical recording of electrical variations detected at the surface of body during their propagation through wall of heart is electrocardiogram.
In the light of above statements,select the correct option given below:

The difference between systolic and diastolic pressure in humans is

The diagram given here is the standard $ECG$ of a normal person. The $P-$ wave represents the:

What is represented by the $P$-wave in an $ECG$?

In all the leads of $ECG$,all following are positive waves except