The results are in Figure D . The experimental design, in engineering units, is not orthogonal. In this case fitted coefficients remaining in the model change as the result of excluding terms from the model. Note how the interaction coefficient has changed. This result gives even more impressive support for Newton's second law.
Coded units are good for seeing the relative size of factor effects.
The effect of a factor is the change in the response due to the change in the factor going from its minimum to maximum experimental value. In the analysis of an orthogonal design using coded units, the regression coefficients are half the factor effect. The plot shown here graphically illustrates this. The acceleration effect is the average difference between the top and bottom values. The mass effect is the average difference between the right and left values.