A review is presented of two original methods of calibrating sources and detectors of optical radiation. Their main feature is that they are absolute, i.e., no calibrated devices are employed. Readings are taken in dimensionless units, i.e., number of pulses per photon, when detectors are calibrated, and number of photons per field mode, when sources are calibrated. A new name is proposed for the latter quantity, namely, the planck, since it is a natural quantum unit of the basic photometric variable, i.e., spectral radiance of radiation. Both methods are based on a nonlinear-optics effect, namely, parametric scattering of light, observed in birefringent piezoelectric crystals such as lithium niobate. The necessary data on this effect are presented together with the theoretical bases of the methods and the results of experimental investigations and comparisons with traditional methods.