Hi, I've been reading the documentation for Boost.Units. I understand most of what it is saying, but am still confused on how to do many things with this library. Most of the examples are using that test_system.hpp. Does this mean that you actually have to explicitly define the units you want to use? I am confused because I see the header files for the units I want to use, e.g., light_year or astronomical_unit, but I can't figure out how to actually use them. If I use boost::units::astronomical::light_second, it cannot find it. I am able to use the SI units just fine, such as: Quantity<si::length> l = 4.0 * si::meters; But beyond that, I'm lost. I also don't know which headers I should include. I don't know if there's one or two headers that include all the basics I would need, or if I have to include each of them individually. Here's a simple program I was trying to write just to test light_second, but do not know how to make it work or which headers to include: int main() { using namespace boost::units; using namespace boost::units::astronomical; using namespace std; quantity<light_second> l1 = 4.0 * light_second; cout << "l1 = " << l1 << endl; return 0; } I'm using Boost 1.41 and I'm on Windows using Cygwin. Thanks, Brandon -- www.creatorspiritus.com Blog and forum discussing living a Christ-centered life Follow me on Twitter: http://twitter.com/devbanana Follow creatorspiritus.com on Twitter: http://twitter.com/creatorspiritus