What is the name given to a time base line on the viewing screen of ultrasonic testing instruments?

The correct term for a time base line on the viewing screen of ultrasonic testing instruments is typically referred to as a "marker." In ultrasonic testing (UT), the time base line serves as a critical component of the displayed signal indicating the arrival time of the ultrasonic pulse as it travels through the material being tested.

Markers on the screen allow the operator to gauge distances, as the time it takes for the ultrasound to return can be converted into depth measurements. This aids in identifying flaws or features within the material by correlating signal responses to specific time intervals.

Using markers enhances the interpretation of the UT data, ensuring that the operator can accurately assess the signal reflection patterns that indicate the presence of defects, the thickness of the material, or other important features. These functionalities make "marker" the appropriate designation for the time base line in this context.