Total Time on Test Plot
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Use a total-time-on-test (TTT) plot to visualize how well your model fits the data. The TTT plot provides a graphical goodness-of-fit test for the power-law process.

·    A power-law process is appropriate if the TTT plot lies close to the diagonal or is a curve that is either concave up or concave down

·    If there is no pattern, or a curve that shifts between being concave up and concave down, the power-law process is inadequate

Below are examples of total time on test plots for improving, stable, and deteriorating systems.