two signals from the two emitters will add up and cancel out however in case there is excessive allowance the signal from the second emitter will be delayed therefore there will be an excessive allowance for a certain time when the two signals are added which will create a peak that will be the signal used for reporting that that link is not within tolerances therefore the behavior is that of a virtual pass no pass gauge this process allows changing the tolerances to be admitted as compliant with the measurements to be checked and it can be used to control any measurement with the sole condition of being able to assemble the corresponding sensors or any other equivalent device to control the total stretching caused in the chains due to accumulated wear of all the links and the wear of the support and guide wheels the first technique can be used and if the data are stored and checked every so often information about how said magnitudes evolve can be recovered in the case of stretching due to wear once the total conveyor length is measured and the number of links is known an average per link measurement can be determined and once known the margin of the tensioning device if.