not sure if I like the name `sec`

could mean a few different things. It would be fine to use if sec only appeared within a few lines of calling `NewSector()`, but it depends on your definition of a few.

If you get too used to truncating variable names you end up with code like x264 where you get 'h', which is defined in some context where it (probably) makes sense, and then used all over the place where there's no such context.