An approximate lookup returns, in a sorted table, the value matching the largest lower bound that is less than or equal to the sought value. It is used for brackets, scales and grading. With RECHERCHEV, it is enabled by the VRAI (TRUE) argument and assumes ascending order; with RECHERCHEX, you use match mode -1 or 1.
Example
=RECHERCHEX(B2;Barème[Seuil];Barème[Taux];;-1)