Homebrew PCBs

At 08:16 PM 07-07-16, you wrote:
>
>
>Impossible to say, it depends on the opacity of your mask and how fine
>your traces are.
>Usually one does a step test, where a strip of mask is withdrawn or
>uncovered step by step in timed intervals, to determine the ideal
>exposure.

My question was about the amount (% or so) of the tolerated 
over-exposure (over the normal exposure), if available, not about
how to determine the right exposure.
Sorry,
Cristian