Hi there, please explain the symbol y here, is it a constant? what does it mean in the equation?

Let us try to take account of education in our theoretical model. We define the productivity-adjusted labour force as Nh where h is the human capital per worker. Suppose further that human capital is determined by h = ers where S is schooling. The derivative of this function with respect to S is dh ds = yers = yh, so we have dh/h ds =Y