User blog comment:BertH/Fluid Editor Preview is now available/@comment-452-20131202180405

I just tested the preview width against the actual width at various resolutions, and it's only correct for the "current" width, and that's only if my browser is maximised (1280px)

It's incorrect at both 784px and 1024px, which are the two "minimum" widths.

Examples:
 * File:Fluid preview test - preview - minimum 1024px.png (current, oops)
 * File:Fluid preview test - saved - window 1024px.png
 * File:Fluid preview test - preview - minimum 784px.png (current, oops)
 * File:Fluid preview test - saved - window 784px.png
 * File:Fluid preview test - preview - minimum.png

edit: Hilariously, I messed up the filenames, but the content of the images is correct.