What does a barometric fuze trigger based on?

A barometric fuze is designed to detonate based on the atmospheric pressure it senses during its descent. This type of fuze is set to trigger when it reaches a specific pressure threshold that corresponds to the altitude of the target. As the device drops, it continuously measures the surrounding air pressure; once it detects that the pressure has decreased to a predetermined level (indicative of a certain altitude being reached), it activates the explosive mechanism.

This method allows for precise targeting, especially in scenarios where the fuze must detonate at a specific altitude to maximize the effectiveness of the ordnance against ground targets. The proper functioning of a barometric fuze hinges on its ability to measure changes in atmospheric pressure accurately, making the option regarding set pressure reached the correct choice.