The latest dependency report shows chrono as having a dependency on math.
See http://www.pdimov.com/tmp/report-develop-3b5a9f4/module-overview.html
math is really big. In testing bpm, an install of timer (which depends on chrono) slowed noticeably when it got to math. Presumably the build is also much slower, although I haven't tested that yet.
Is the math dependency really needed?
Longer term the better solution would be to repackage Math as several smaller packages. However, Paul and I have worked hard to try to make a wide range of functionality part of a coherent whole, and I would hate to loose that. Which is my plea to not just hack it apart in a hurry ;-) Of course since we haven't had any kind of package management until now, this has basically been a non-issue up till now. John.