Which approved anemometer is not omni-directional?

The correct response to the question identifies the Turbometer as the anemometer that is not omni-directional. An omni-directional anemometer can measure wind speed regardless of its direction, meaning it can provide accurate readings from any angle. The Turbometer, on the other hand, typically measures wind speed and direction based on specific orientations or setups, which makes it not omni-directional.

In contrast, the other options, including the DIC-3 and AN/PMQ-3A, are designed to measure wind speed effectively from all directions, adhering to the characteristics of omni-directional instruments. This distinction clarifies why the Turbometer does not fit the criteria of being omni-directional while the others do.