Final answer:
The over-direction used when cutting a square one length below the shoulders is forward over-direction.
Step-by-step explanation:
When cutting a square one length below the shoulders, the over-direction used is called 'forward over-direction.' This means that the hair is pulled forward and cut slightly shorter than where it naturally falls when left to hang straight down.
By using forward over-direction, the hair is given extra length in the back and creates a square shape when cut. This technique is commonly used to achieve a square-shaped one-length haircut below the shoulders.
For example, if the client's hair naturally falls right at their shoulders, using forward over-direction would involve pulling the hair forward to cut it slightly above the shoulders, resulting in a square-shaped haircut.