Measuring Fork Width

[BigIron]

I was looking at windshields on ebay from cycleshields and in the description it says to measure the fork tube diameter and width. Now I understand the tube diameter but how is the width measured? Is it center to center or from the two outermost points? I emailed the guy with my question a few days ago but no reply.

Also,
I like the looks of that Plexistar2 shield because it would provide better cold weather protection for my hands/arms (fork width not an issue on this one). However, If someone were to drop the bike, wouldnt it be more prone to breakage since its as wide as the bars? This question is what got me looking at the narrower shields.