The concentrations of IAQ contaminants almost always fluctuate over time. Therefore is it best to log data over time, whenever possible. Technology, and more importantly, budget constraints may prevent us from logging data over time. That means we must show up on a given day and measure that point in time. This method gives us a random reading from a normal day.
If we only have one shot at taking a measurement, some advocate aggressive sampling to simulate the absolute worst case maximum scenario. Let me give you some examples of trying to simulate the worst case maximum scenario: