Instrumentation and calibration at the ESRF

The degree of precision to which we can hope to measure a survey network is dependent upon its configuration and the instrumentation used to measure it. At the ESRF considerable efforts have been made to improve instrument precision and in particular distance measurements by means of calibration, COFRAC accreditation under the ISO/CEI 17025 Norm has ensured that the greatest rigor be applied in the calibration techniques used at the ESRF. Measurements have shown that in order to improve upon alignment accuracy, we must now make an effort to improve angle measurement precision. We are presently developing an angle calibration method that will reduce those errors associated with an observed distance dependence. (author)