Thanks for the comments everyone. Dennis I was determined to get the perihelion Sun that day those clouds weren't going to stop me!
Dean I tried the measurement myself (about) 576 pixels/596 pixels = 96.6%
147.1 million km/ 152.1 Million km = 96.7%
I didn't really know how the comparison would look when I took the second pic and I'm glad it seems to be consistent!
I had fun trying to work out how best to display it too.
Cheers,
Tom