Wiktionary
step function
n. (context mathematics English) A function from the real line to a finite subset of the real line.
Wikipedia
Step function
In mathematics, a function on the real numbers is called a step function (or staircase function) if it can be written as a finite linear combination of indicator functions of intervals. Informally speaking, a step function is a piecewise constant function having only finitely many pieces.
Usage examples of "step function".
But the step function makes it plain that something passed through the ring from above to below.