I'm looking at training surcingles on eBay. They seem to be measured in inches and the ones I'm looking at (admittedly the low end price-wise) look to be 60"-68".

But I seem to remember that when I was calculating my horses' weights a few months ago, their heartgirth measurements were similar to their blanket measurements (I joked that they were square). So heartgirth of 74"-80". What am I missing here? Are they measuring two different things? Does a surcingle go enough further back on the horses back as to cut off 12-14 inches or so from the measurement?

I just wanted to order this from work without having to go home and measure *stomps feet* but even more to the point, if I measure my horse at 78" like I think I will, how does that jibe with the surcingle sizes I'm seeing?