In inertial confinement fusion experiments, a fiducial system is established in order to correlate the signals from different channels of one spectrometer and the signals from different spectrometers to obtain time-related experimental data. The constitution, the principle and the data processing method, together with the uncertainty analysis are introduced. Signals from different channels and from three spectrometers diagnosing from different directions are correlated with an uncertainty of 70 ps. The time-related historical radiation fluxes from a cylinder target, measured from three different directions, are obtained in the experiments on Shenguang Ⅲ prototype laser facility, offering the physical information about the heat wave propagation along the axis of the cylinder and the attenuation of soft X-ray radiation flux.