The Secular Decrease of the Crab Nebula at 927 and 151.5 MHz

Long-term measurements have been carried out of the Crab Nebula radio emission flux density relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. As a result the mean rates have been found of the secular change of the Crab Nebula radio emission flux density: $d_m (927\hbox{MHz})=-(0.18\pm0.10)$% year$^{-1}$ (over the period 1977--2000), $d_m (151.5\hbox{MHz})=- (0.32\pm0.08)$% year$^{-1}$ (over the period 1980--2003).