A.3.3.PI:4.3 - Choose the least costly useful repair

Use the missing distinction to choose a repair.

• Retain additional state values. Keep component amounts, velocity, operating mode, pending input or another variable whose difference changes the result. Include a way to obtain or estimate it in the intended use.
• Retain relevant history. Use observations and intervening actions to infer the missing state or construct a direct recurrence. Derive the needed history length from the rule and observation account where possible.
• Retain an uncertainty account. Carry the admitted state set or a distribution over possible states and propagate it through the rule. Use probability weights when a probability model is supplied.
• Answer a weaker question that still serves the work. A range, threshold decision or shorter-horizon result can be sufficient even when a unique future value remains unresolved.

Compare the available repairs by what they change in the decision and by their cost. C.11.DUA helps decide whether another measurement or calculation is worth obtaining. Use an already adequate bound directly.

A finite history can close some models, including the two-substance example. Other projections need a longer history, an approximate memory account or retained uncertainty. Choose the repair from the dynamics and the intended error, rather than assuming a fixed number of observations always reconstructs the state.