A system for measuring a changing crack, comprises: a measurement device comprising a body bearing a measurement instrument and having a first positioning means, and a movable member comprising a second positioning means; at least two targets that are able to cooperate with a positioning means, wherein the at least two targets are hemispherical in shape and wherein the positioning means consist of rings having a cross section that is smaller than the base section of the target.

An automatic measuring device includes a micrometer including a spindle that moves forward and backward to be brought into contact with or away from a workpiece and a displacement detector unit that detects displacement of the spindle, and an automatic operation unit that automates the forward and backward movement of the spindle by power. The automatic operation unit performs a first forward-movement step of moving the spindle forward to bring the spindle into contact with the workpiece, and a contact determination step of determining the contact between the spindle and the workpiece in the first forward-movement step. In the contact determination step, the spindle is determined to be in contact with the workpiece when a change in a position of the spindle detected by the displacement detector unit in the first forward-movement step becomes equal to or less than a predetermined contact determination threshold.

An automatic measuring device includes a micrometer including a spindle that moves forward and backward to be brought into contact with or away from a workpiece and a displacement detector unit that detects displacement of the spindle, and an automatic operation unit that automates the forward and backward movement of the spindle by power. The automatic operation unit performs a first forward-movement step of moving the spindle forward to bring the spindle into contact with the workpiece, and a contact determination step of determining the contact between the spindle and the workpiece in the first forward-movement step. In the contact determination step, the spindle is determined to be in contact with the workpiece when a change in a position of the spindle detected by the displacement detector unit in the first forward-movement step becomes equal to or less than a predetermined contact determination threshold.

A micrometer head displacement system includes a micrometer head and an imaging portion. The micrometer head includes a coarse scale and a fine scale. The system is configured to: acquire at least one image of the micrometer head from the imaging portion; determine a coarse measurement based at least in part on the at least one image wherein the coarse measurement corresponds to a coarse relative position between the coarse scale and a coarse fiducial line; determine a fine measurement based at least in part on the at least one image and based on calculating an interpolated position of the a fiducial line wherein the fine measurement corresponds to a fine relative position between the fine scale and the fine fiducial line; and determine a micrometer head displacement based at least in part on summing the coarse measurement with the fine measurement.

A micrometer head displacement system includes a micrometer head and an imaging portion. The micrometer head includes a coarse scale and a fine scale. The system is configured to: acquire at least one image of the micrometer head from the imaging portion; determine a coarse measurement based at least in part on the at least one image wherein the coarse measurement corresponds to a coarse relative position between the coarse scale and a coarse fiducial line; determine a fine measurement based at least in part on the at least one image and based on calculating an interpolated position of the a fiducial line wherein the fine measurement corresponds to a fine relative position between the fine scale and the fine fiducial line; and determine a micrometer head displacement based at least in part on summing the coarse measurement with the fine measurement.