If the pre-compiled extension module that is included in the sources does not work for you (in that case you'll notice that the movable measurement window's size does not closely match the size of the borderless window generated by ArgyllCMS during display measurements) or you want to re-build it unconditionally, run python2 setup.py build_ext -i to re-build it from scratch (you need to satisfy the requirements for compiling the C extension module first).