Ok, I have been saddle shopping and this has finally up enough for me to look for outside answers.
One lady selling the one of the saddles I was looking at measured from the back edge of the button and it measured 17.25" and she said it was a 17" seat. I measured it from the center of the button and it measured a easy 17.5".
On another saddle the person selling had one advertised as a 18". The picture looked like they were measuring from the center and it measured 17.75". I suspect if you chose to measure from the front or back it would measure as a 17.5" or 18".
How do you guys measure, front of the button, center, or back? These were the same brand but different models. I have seen some brands use big button heads and that could make even more of a difference. I have also run into this problem when I have been selling saddles, folks say I am measuring wrong, misrepresenting the saddle, etc.
On a side note, I really wish saddlers would just mark their sizing on the saddles that they make and not on the bullet guards that are easily removed. I mean really how hard could that be.