The model EDJ-41M is used for monitoring of cracks, joints and fissures.It consists of two stainless steel round datum blocks that are installed on either side of the opening. Each datum block has a groove on the surface along the circumference to assist in taking readings. A through mounting hole helps mounting the datum block on concrete, masonry or rock surface using expandable anchors. M8 nuts are provided to tighten the expandable anchor. The distance between the grooves of the datum blocks is initially measured by a digital inside caliper with a resolution of 0.01 mm.