2.5 mm. It is easy to explain why it not getting wide than why it is getting taller The atrial vector has two components. The initial RA vector, is directed anteriorly. The main reason is due to the anatomical proximity of RA to the chest wall. Fuher the atrial electrical dp/dt is fast, so the slope of forward limb is steep. Any RA voltage increase is easily picked up by the chest leads. LAE can not produce tall P wave The left atrial vector which follows RA vector is mainly directed posteriorly and hence inscribe a descending limb of P wave. This causes the P terminal force. So the direction of vector forces and the anatomical locality make a tall and positive P deflection highly improbable in LAE.">