This custom grid was developed to support our 2015 ad footprint where we introduced all IAB standard ad units (Leaderboards 728x90 and Medium Rectangles/Box Ads 300x250). Margins were added on either side of the grid for the purpose of protecting our pages from the occasional custom wallpaper ad or browser edges.

When designing to the grid just remember that everything needs to be horizontally divisible by 5 pixels, so no 37px gutters.