In reality, we have an infinite number of possible bell-shaped curves, and not only the standard curve.

Each probability distribution has its own expectation and standard deviation, and therefore its own bell-shaped curve. Our ability to calculate probabilities for standard normal distributions is of no use to us (for now) in calculating probabilities for other bell-shaped curves, while these account for most of the actual cases. But the mathematicians have come to our aid again.

They have found a way to turn any normal probability distribution (the target curve) into the standard normal probability distribution.

This method is called standardization. Standardization is actually a kind of translation of the values of any normal probability distribution into values corresponding to the standard bell-shaped curve (= the standardized values), which enables us to use the table.

It therefore follows that almost any problem we want to solve will include two separate operations:

Standardization.

Searching in the table.

The standardized values are called standard units.

The standardization operation represents the process of translating the target curve into the standard curve.