Locate the z-score of the data value and use a Z-Score Table to find a specified area under a normal curve. On a standard normal distribution, a Z-Score Table indicates the proportion of values (or area percentage) to the left of a given z-score. On a conventional normal distribution, a z-score table indicates the percentage of values (typically a decimal number) to the left of a given z-score.
For instance, take a Z-Score to be 1.27. We first look at the left side column of the standard 2-table to find the value corresponding to one decimal place of the z-score.
In our case it is 1.2. Then, we look up the remaining number across the table which is 0.07 as depicted in the table below.
Therefore, the corresponding area is 0.89796 which translates to 89.796 of the standard normal distribution as depicted below.