The trendline is obtained by linear fitting in Excel. The R2 value is the so called correlation coefficient which is always between 0 and 1. If it's exactly 1, the relation between the variables is exactly linear. If it's zero there is no linear relation between the variables. In our case, it is pretty much to 1, so I'd say it's a straight horizon anytime. Grin
I don't understand the point of testing this. Imagine making a 360 degree panorama,
how could it curve the way you're testing it?

The curve goes away from the point
of reference in all directions (if you believe in RE).
Also, you seem to have the terminology mixed up. R2 is the coefficient of determination and
measures the fit, which in simple regression happens to be the degree of linear relationship.
The correlation coefficient ranges from -1 to 1, and shows the degree of positive or
negative correlation. The square of the correlation coefficient yields R2 in simple regression.
Let me be clear that I'm not trying to offend you, and I'm also aware of you being an RE'er.