Callback custom function when a slider is updated [2.79]

Hello there,

I’m coding a simple panel in the 3DView.
I want to be able to call a function when I change a custom property value by moving a slider.

Were should I start ? I haven’t found anything useful in the API doc but It’s hard to find something that you don’t know of.

I give you a screenshot of what i’m working on.

Thanks