A normal curve in which the X scale is converted into the Z scale on which the Mean (m) is taken at a 0 and the standard deviation (σ)
is taken at a unit is called a standard normal curve. This way of conversion of a normal curve into a standard normal curve is called Z-transformation. This sort of transformation is done with a view to facilitating the work of finding out the area between the various ordinates without any difficult which is very much felt when different normal curves appear with different values of Mean, and Standard Deviation.
The following figure exhibits the specimen of a standard normal curve identified as above: