Calibration Base Line Program

EDMI Calibration Base Line Program

NGS conducts a cooperative program that provides surveyors with a means to detect and correct errors in Electronic Distances Measuring Instruments (EDMI). NGS has established more than 400 EDMI Calibration Base Lines (CBL) throughout the United States in cooperation with various government agencies, universities, professional societies, and others. These highly accurate base lines provide a locally accessible standard for length measurement. For each state, NGS provides users with location descriptions and the adjusted results of calibration base line measurements.

  Find Data by State:


Online Resources:

    NOTICE! In an effort to make the NGS EDMI CBL Program sustainable and more useful for our partners and customers, NGS is considering significant policy and procedural changes to the program.


  • The proposed, revised program policy (in draft form) is found in CBL Program Policy 9-9-2016.
  • The proposed, revised procedures (in draft form) to implement the program are found in CBL Program Procedures 9-9-2016.
  • A Federal Register Notice on the policy and procedure changes is available.
  • Feedback regarding the proposed policy and procedural changes is due by close of business Tuesday, January 17, 2017 and can be provided directly to NGS using the following email address: ngs.feedback@noaa.gov
  • Note: On November 10, 2016, a webinar was held to address the draft changes to the policy and procedures document, and to solicit feedback. For clarification to an audience question posed during this webinar regarding any restrictions concerning slope along a proposed CBL range - refer to NOS NGS 8 Establishment of Calibration Base Lines, page 8: "To ensure uncertainties of computed horizontal distances fall within acceptable tolerances, the slope between monuments should not exceed three percent".
  • Calibration Base Line data are available online. The file naming convention consists of a two letter U.S. state code for current data. Files with an extension of .his consist of CBL historic data.
  • PC software CALIBRAT (Windows 32-bit only) is used to determine the scale and constant corrections for electronic distance measuring instruments by making measurements over previously determined base lines. The formulas used in the program are found in NOAA Technical Memorandum NOS NGS-10: Use of Calibration Base Lines.
CBL Publications: