What does the term 'lock' refer to in radar speed measurement?

In the context of radar speed measurement, the term 'lock' refers to the process of capturing a specific speed reading and maintaining that value until the device is reset or a new measurement is made. When the radar unit is "locked," it means that the device has successfully detected and stored the speed of a vehicle that is within its range, providing the operator with a reliable data point for enforcement purposes. This functionality is crucial for law enforcement, as it establishes a verified speed at which the radar has detected a vehicle, ensuring accurate readings that can be used in legal situations. The ability to lock onto a speed also helps in minimizing erroneous data, as the radar system can filter out background noise and focus on a specific target.

The other options, while relevant to radar operation, do not accurately capture the concept of 'lock' in this context. For instance, turning off the device, initiating a speed measurement, or disabling false signal detection, all refer to different functions or operations that do not relate to the immediate process of capturing and holding a specific speed reading.