User blog comment:Kirkburn/Technical Update: July 1, 2015/@comment-18172179-20150704230116/@comment-452-20150705045325

I checked that page and your Desktop screenshot does not match what I am seeing.

The preview you have posted is accurate to what I see, but here's my own screenshot anyway:

For reference, my screen is 1280px, and my browser is maximised.

As shown in my screenshot, and your preview screenshot, Desktop has a article width of 704px. Your boxes are 244px each, counting border and margin, so 3 across would require 732px.

I'm not sure why you're seeing it as slightly wider - do you have any CSS customisations?

edit: Your Desktop screenshot shows the blue area as 1238px - that's exactly the "Desktop XL Content Space Width" quoted in User_blog:Rupert_Giles/Layout_Changes:_Breakpoints_and_Typography. So, you are a Desktop XL user. What is your screen resolution?