Documentation for compiling scss?

Im trying to customize some css and I can t seem to get the scss file to compile. Any tips?

$ compass watch --trace
LoadError on line ["36"] of c: cannot load such file -- modular-scale
  c:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'

  c:/www/sandbox/sites/all/themes/ember/extensions/ux_styleguide/lib/ux_styleg
uide.rb:6:in `<top (required)>'
  c:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'

  c:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'

  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:7
5:in `block in register_directory'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:3
9:in `detect_registration'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:7
4:in `register_directory'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:6
3:in `block in discover'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:6
2:in `each'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/frameworks.rb:6
2:in `discover'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/configuration/h
elpers.rb:118:in `discover_extensions!'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/commands/projec
t_base.rb:27:in `configure!'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/commands/projec
t_base.rb:15:in `initialize'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/commands/update
_project.rb:37:in `initialize'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/exec/sub_comman
d_ui.rb:42:in `new'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/exec/sub_comman
d_ui.rb:42:in `perform!'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/lib/compass/exec/sub_comman
d_ui.rb:15:in `run!'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/bin/compass:30:in `block in
 <top (required)>'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/bin/compass:44:in `call'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/compass-0.12.2/bin/compass:44:in `<top (re
quired)>'
  c:/Ruby193/bin/compass:23:in `load'
  c:/Ruby193/bin/compass:23:in `<main>'