There may be an increasing random error in the measurement. 

There may be a nonlinear sinusoidal relation between independent variable X and depend variable Y.

There may be a time-depended error in the measurement. 

There are outliers in the measurement. 

There may be a sinusoidal error in the measurement. 

Residuals follow the Normal Distribution

Residuals are not correlated with time

Residuals are not correlated with independent variable X

Residuals have a constant variance

Residuals should be normal distributed

Residuals should not be correlated with X

Residuals should not be correlated with Y

Residuals should have constant std

Each Residual should be independent and follow

the same distribution