Locate the spot for the occurrence you want to determine the probability of along the Y-axis. For example, if you are using a craps probability chart to look up the likelihood of rolling a five then read along the Y-axis for the label that says "five."
Follow along the line perpendicular to the Y-axis until you find the marker indicating the position of that particular occurrence. For example, if you look out from five on the Y-axis, you continue moving right until you hit a marked point.
Look directly beneath the point to find the X value for that occurrence. For example, if you hit the point that marks the probability of rolling a five in craps and look directly down, you would find that point is at the X value 4/36, or 1/9.
Record the X value as the likelihood of that event occurring.