Add to a float value with a button?

I have a menu with a scroll rect, so it’s a scrolling list of buttons. I want the button to subtract .015 to scrollrect.vertizalNormalizedPosition, so you can scroll down the list of buttons by pressing this scroll bar button. Is there an easy way to add to a value when a button is pressed, instead of just assigning a set value?

What about this?

public void ScrollUp()
{
    scrollRect.verticalNormalizedPosition -= 0.15f;
}

public void ScrollDown()
{
    scrollRect.verticalNormalizedPosition += 0.15f;
}

And then in one button asign ScrollUp() function, and in another asign ScrollDown() function