why is udf called again and again?

Hi experts,

I have been puzzled by the working mechanism of the UDF. Why is a udf called again and again by acuSolve even in a single time step? Is that because the solver has to solve related equations at different quadrature points? Is a udf called as many times as there is number of quadrature points??? But I see even in a single time step, a quadrature point is invoked multiple times. Any hint on this???

Thanks!!!