Patent ID: 7024793

Claim:
A caliper usable to measure tree diameters, said caliper comprising: a graduated rule along which a slide is movable, a first leg attached to one end of said rule and a second leg attached to the slide, wherein measuring of said diameter is effected between said legs, an electronic unit for measuring the position of the slide along the rule and for storing measurement values and other desired data, wherein the graduated rule includes a longitudinally-extending internal cavity and a part of the slide located on the rule includes a permanent magnet; a measuring element including an electrically-conductive wire extending within said cavity and attached at both ends to said rule, which wire co-acts with a piezo crystal adjacent said one end of the rule; wherein the respective ends of said wire are connected electrically to a pulse generator which generates short electrical pulses of predetermined duration; and wherein the caliper includes detector means which co-acts with the piezo crystal to detect a geometric change in the wire, wherein said piezo crystal emits an electrical pulse in response to said geometric change.