The GPS pole is a constant height of two (2) meters. By always knowing the exact height of your system, you will have a higher degree of accuracy and fewer errors in either incorrectly recording the number or forgetting it all together.It is constructed so that there are no variations in height other than that of the replaceable tip point through usage. The three telescoping legs, two of which are a quick release system, will extend over 10 feet. Can be used as bi-pod or as tripod. On the center leg approximately 40" above the tip are 3 level vials mounted 120 apart. This assures that the pole heights and horizontal positioning are within +/- 1mm accuracy. The GPS pole was created for, thoroughly tested, and approved by the NGS in Cordin, VA. In addition, see GPS book, A Comprehensive Guide to Land Navigation.