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In a high-tech assembly plant, total production is represented by the continuous function P(T, M), where T denotes technician labor input, and M denotes machine capacity.

When demand increases, but the budget remains fixed, the manager must determine which input will enhance production more efficiently.

To make this decision, the effect of each input is analyzed separately. First, the impact of increasing technician labor is examined with machine capacity fixed.

This is measured by the partial derivative of P with respect to T, which shows the instantaneous rate of change in production as technician labor increases at current operating conditions.

Next, the effect of increasing machine capacity is examined while holding technician labor constant.

This is measured by the partial derivative of P with respect to M, which represents the instantaneous rate of change in production as machine capacity increases at current operating conditions.

By comparing these marginal contributions, the manager can identify the more effective investment.

A partial derivative measures how a function changes with one variable while others remain fixed.