Incorrect Slope

I am using Office 2007, and I have run into an interesting problem. I noticed when I ask excel to display the equation of a linear trendline that it gives me an incorrect slope. The y-intercept is correct, but the slope is not correct. For example:

If I plot the points (.5,.5) and (1,1), I am given a slope of 0.5
If I plot the points (10,10) and (20,20), I am given a slope of 10
If I plot the points (1,1) and (2,2), I am given a slope of 1

These are all equations of the form y=1x+b. The slope should clearly be 1!

I have tried plotting the same points and trendlines on a different computer (also Office 2007) and there was no problem displaying the correct equations whatsoever. Does anyone have any idea why this is occurring on my computer? Perhaps I toggled a setting somewhere?