What is the difference between 2x and 4x sample buffer? - SDS Sample buffer (Mar/01/2002 )

Hi
I'm running SDS gels, I want to make up a 4x sample buffer.  Do I just make up the 2x recipe in half the final volume?

thanks

here's a recipe for 4x from gibco

4x Sample buffer for (non-reduced gel): (for 10 mls use)
      12% SDS              1.2g
      40% Glycerol        4.0 ml
      0.2 M tris-HCl pH7  2.0 ml of 1 M Stock
      0.004% Bromophenol Blue  0.4 mg

4x Sample Buffer (for reduced gel):
Same volumes and amounts as #1 above but add to
solution 0.5 ml 2-Mercaptoethanol.