A method to calibrate in an absolute way the solid state detectors that are used to monitor the muon flux in the (anti)neutrino beam line at the CERN SPS is described. This calibration is one way that opens the possibility to measure the (anti)neutrino flux needed for the determination of the absolute total cross-sections of (anti)neutrino-nucleon interactions. Tracks of charged particles are recorded simultaneously in the solid state detectors and in Ilford G5 emulsions. The readings of the detectors are compared with a count of the tracks in the developed emulsions. Absolute calibration factors (number of passing muons per delivered pC of electric charge) under particular circumstances are given. The overall accuracy that can be obtained is 3%.