Excel slope function vs linest function

To get the slope of a pair of x and y, usually I first plot the curve and then add the trend line.

 

Actually there are two functions in Excel to help me do this. The first one is the 'SLOPE' function. However, it only gives what is shown by the red trend line (slope=0.25). The second one is 'LINEST' function, which is more flexible. By setting the third parameters in the function to 'False', it automatically set the intercept to zero (slope=0.36).

'LINEST=(y series, x series, False)'