slope function returns different value as the trend-line equation

Hey all,

I don't know if I found a bug or if there is something weird that I did. But I'll share this anyway.

I am using numbers to find the rate of oxygen coming into wine closures. (collecting lab data on numbers for the ipad is soooo easy by the way)

Anyway, amongst my measurements, what I am really interested in is the rate at which they change - the slope of the line.

I noticed that if I use the Slope() function I get one number - but if I add a linear trendline and show the equation, (y=mx+b where m is the slope) the slope in that equation is a different value than what the slope function gives me.

I ported the data over to excel and ran the same exercise - the equation on the chart versus the slope() function - and over there, the two numbers match as they should.

I have a feeling that the problem might be with the generation of the xy/scatter chart itself, because the maxima on the x axis when I chart it all out is less than the same from the data ( I have data over 4 and the chart shows the last readings just below 3.

If the axes are off then that would explain the wrong slope. But then why is the x-y chart wrong, and if it is not a bug and I'm doing something wrong, I'd like to figure it out because I use these x-y charts quite a bit.