How is the time weighted mean (TWM) calculated?

The time weighted mean (TWM) is calculated by weighting data based on the duration of time each data point is relevant. This approach ensures that longer periods of time exert more influence on the overall average. In this context, multiplying stay times imposed across areas reflects the concept of timing and duration in the calculation process.

When certain areas or conditions are assessed over different time spans, the data collected must reflect the length of time those conditions were present to obtain a meaningful average. By considering these stay times, the TWM effectively incorporates the temporal aspect of the measurements into the calculation, allowing for a more accurate representation of average conditions over time.

The other choices do not accurately represent how a time weighted mean is derived. For example, using average temperature over time does not account for the duration of each temperature reading; instantaneous temperature readings would not reflect ongoing conditions; and simply adding all cooling periods does not take into consideration how long each period lasted in relation to others. Thus, acknowledging stay times aligns with the principles of time weighting crucial for accurately calculating the mean.