Qt 4.8.5 is highly recommended.

If header (h) or interface (ui) files have changed, please perform
a distclean before building Spot-On.

Absolute cleaning:
make distclean or mingw32-make distclean

FreeBSD:
qmake -o Makefile spot-on.freebsd.pro
make

Linux:
qmake -o Makefile spot-on.pro
make

OS X:
qmake -spec macx-g++ -o Makefile spot-on.osx.pro
make

Windows:
qmake -o Makefile spot-on.win.pro
make or mingw32-make
