Final answer:
The measurement of vacuum for a system should be done when the system requires a low-pressure environment. In freeze-drying foods, the vacuum speeds up dehydration by lowering the boiling point of water in the food. Dehydration is considered complete when the weight of the food stops decreasing.
Step-by-step explanation:
The measurement of vacuum for a system should be done when the system requires a low-pressure environment. For example, in the process of freeze-drying foods, a vacuum is used to dehydrate the food. The vacuum speeds up dehydration by lowering the boiling point of the water in the food, causing it to evaporate more quickly at lower temperatures. To know when dehydration is complete, one can monitor the weight of the food over time. Once the weight stops decreasing, it indicates that the food has been sufficiently dehydrated.