This report describes the procedure currently applied for the calibration of the load cells used for the mechanical experiments in the ELSA laboratory. The procedure is based on the international norm ISO 7500-1 and the definitions there proposed. The calibration experiment consists of applying a number of load cycles simultaneously on the object load cell in series with a traceable measuring proving instrument externally calibrated (reference load cell). The accuracy of the measures of the object load cell is the most important result of the test delimiting the maximum difference between both instruments. Other important results of the test are the resolution, repeatability and reversibility of the object load cell. All these error parameters determine the quality of the object instrument at the state of the calibration test. In order to extend the validity of the calibration test to the experiments performed with that load cell when connected to amplifiers different from the one of the calibration test, an additional gain test of the signal conditioning chain is also undertaken at ELSA after the calibration test.