We now realize why accurate control of the assembly process is so difficult. We would have to predict or control such unpredictable things as the friction forces between parts, the effort required to pull the joint together, the amount of hole interference, and the elastic interactions between bolts to achieve exactly the same amount of residual preload in each bolt. I think that it’s safe to say that we’ll never be able to afford the effort the required to predict or control the many variable involved. This does not mean, however, that all is lost.