Why would the stt shape change while in the same lead? could 1 j point notch in leads i,ii and iii affect other leads? as the ecg goes to the right the end point is 1-3 boxes lower?

Abnormal ECG: A 12 lead ECG has commonly 2-3 complexes per lead. Changes in ST/T segments in different complexes should not occur in the same lead on the same ECG unless there is a different origin to a beat (ex. PVC, PAC). The mechanism that causes a J point abnormality is systemic through an ECG, and could be seen variably on other leads. Not really sure what is meant by "end point" in the last question.

Needs more detailed : Variability in the ST segment from beat to beat in the same lead may be an artefact due to patient movement. Changes in the ST segments in several consecutive beats in the same lead could be of significance. The ECG should be recorded by a technician who is adequately trained in the recording of the ECG. Proper application of the electrodes and avoidance of patient movement are crucial.