Residual torque can be measured using a power tool hooked up to a rotary transducer and torque analyzer. However, residual torque is most often measured using a transducerized electric wrench, a dial wrench or a preset hand tool, such as a click wrench or slip wrench. A click wrench has a calibrated mechanical cam that resists movement until a set torque is reached. A dial wrench has a spring that translates torque into motion on a calibrated dial. Fastening experts warn that residual torque and dynamic torque are not identical.
Residual torque is often lower than dynamic torque.
In many cases, the joint relaxes after being fastened. Joint relaxation occurs to some extent in all fastened joints. One part embeds into another. A layer of paint, a spring washer or a soft part, such as an O-ring, compresses under the clamp force. This relaxation, or creep, is most obvious and dramatic right after force has been applied.