To determine the ST elevation, it is important to know where to measure the ST segment from. For that, you need to find the J point. If you follow the QRS complex on your ECG, you will see that they are usually sharp-pointed. If you go down with the Q wave, up with the R wave, down the S wave and follow the S wave back to the baseline, it will usually pass the baseline. The moment that line goes horizontal, that is where your J point is. You need to find the J point and then measure the distance between the baseline and the J point. If that distance is more than two little blocks in the precordial leads (in other words, two millimetres) - or more than one little block in the limb leads (in other words, one millimetre) - then we say the ST segment is elevated.