they stack additively, so just add up the crit chance.  1 PD will increase your total crit chance by +30%.  The 2nd PD will increase your total crit chance by +30%, so +60% crit chance total from 2 PD's.

How does critical strike chance stack?
I have "library" folder with multiple object (.o) files. These files contain subroutines which are not changing from project to project. Each new project uses some of those object files, but not all of them.
Could you please tell me is there any way to tell gfortran to look up that folder for necessary .o files?
I've tried -I and -L options, but no way. When I write .o names directly, it works:gfortran main.for ./library/obj1.o ./library/obj2.o but I have many of .o files and write all of them waste time.
I could write gfortran main.for ./*.o but then main program will be linked with all .o files, but it needs only some of them.
I hoped that something like gfortran main.for -L./library/ will work, but it doesn't.
I use OS X with gcc version 5.1.0.
And I'm pretty sure that I should use makefile for such case
