View/Actual,Fitted,Residual - it is quite strange

[quoctruongphan]

Hello all,

After constructing a simple linear regression, I go to View/Actual,Fitted,Residual >> Actual, Fitted, Residual Graph.

It is quite strange that the Fitted Line is not straight. To my knowledge, since this is linear regression, it is supposed to be straight, not a line with so many break. I don't understand why and hope someone could help me interpreting this matter.

I attach Eview file, just click on eq01.

Thank you for reading,
Regard,

[startz]

The graph has an axis of observation number, not the right hand side variable.