ISO 17123-2:2001

Overview - ISO 17123-2:2001 (Levels)

ISO 17123-2:2001 defines practical field procedures for testing levels (spirit levels, compensator levels, digital levels) used in geodetic and surveying work. The standard provides in situ verification methods to evaluate the precision in use of a level and its ancillary equipment under realistic field conditions, without requiring specialised laboratory rigs. These procedures are intended as field checks of suitability for an immediate task and as initial steps toward assessing measurement uncertainty (in line with the GUM), not as full acceptance or exhaustive performance tests.

Key topics and requirements

• Two test procedures
  • Simplified test procedure: quick field check (suitable for building/site levelling). Uses two configurations (approx. 60 m between points) and two sets of 10 measurements to compare equal and unequal sight lengths.
  • Full test procedure: rigorous field test for higher-precision levelling (civil engineering/linear surveys). Uses equal sight lengths (recommended 30 m, variation ≤10 %) and yields an experimental standard deviation expressed as the 1-km double-run levelling precision (sISO-LEV).
• Environmental and setup guidance
  • Choose a reasonably horizontal, uniform test area; avoid hot surfaces (asphalt/concrete) when possible.
  • Allow instrument acclimatisation (~2 minutes per °C difference) and shade the instrument in direct sunlight.
  • Check collimation error per manufacturer’s instructions before testing.
  • Use stable, fixed levelling staffs and appropriate tripods as recommended by the manufacturer.
• Measurement and statistics
  • Procedures specify sequences of forward/backward readings, lifting and slightly repositioning the instrument between measurements.
  • Simplified method produces mean differences and residuals; full method provides the experimental standard deviation and statistical tests to compare measured precision against theoretical or between samples.
• Purpose and limitations
  • Designed to minimise atmospheric refraction effects and to be executable without special ancillary equipment.
  • Intended as the first step in uncertainty evaluation; comprehensive uncertainty assessment requires follow-on analyses (GUM, reproducibility, error-source assessment).

Practical applications and users

Who uses ISO 17123-2:

• Surveyors and field engineers performing routine levelling checks on construction and infrastructure projects
• Quality managers and site supervisors verifying instrument suitability before measurement campaigns
• Metrology and calibration teams performing in-situ precision checks of optical and digital levels
• Instrument manufacturers and testers validating field performance under project-relevant conditions

Benefits:

• Fast, standardised field verification of levelling precision
• Helps ensure measurement suitability for tasks ranging from general site levelling to higher-precision engineering surveys
• Provides documented, repeatable methods that support measurement quality control and traceability

Related standards

• ISO 17123-1 (Theory) and other parts of ISO 17123 (theodolites, EDM, tacheometers, etc.)
• ISO 4463-1 (measurement planning and acceptance criteria)
• GUM (Guide to the expression of uncertainty in measurement), VIM, ISO 7077, ISO 7078, ISO 9849, ISO 3534-1

Keywords: ISO 17123-2, levels, field procedures, testing geodetic and surveying instruments, levelling, experimental standard deviation, collimation, measurement uncertainty, simplified test, full test.