What is a common tool used for measuring joint flexibility?

A goniometer is a specialized instrument used specifically to measure the range of motion at a joint, which directly relates to joint flexibility. It allows physical therapists and other healthcare professionals to assess the angles of movement in joints, giving valuable information about the extent of flexibility, any restrictions, and overall joint function. By measuring the degrees of movement, practitioners can track progress over time, establish treatment goals, and adjust rehabilitation plans as necessary for optimal patient care.

The other choices do not serve the purpose of assessing joint flexibility. A thermometer measures temperature, a caliper measures distance between two opposite sides of an object, and a manometer measures the pressure of gases or liquids. None of these tools provide the angle measurement needed to evaluate joint motion, making the goniometer the appropriate and commonly used instrument in this context.