In the early 1980s CCD cameras appeared, and the number of SNe discoveries increased substantially. Moreover, the probability of discovering SNe before they reached maximum light and following their brightness evolution longer also increased. The first light curves of SNe Ia obtained using CCD photometry showed that some supernovae had faster decline rates than others. Later, the low luminosity Ia SN 1991bg with a fast decline rate was discovered. All this motivated the American astronomer Mark M. Phillips to revise this relationship precisely during the course of the Calán/Tololo Supernova Survey. The correlation had been difficult to prove because Pskovskii's slope (β) parameter was difficult to measure with precision in practice, a necessary condition to prove the correlation. Rather than trying to determine the slope, Phillips used a simpler and more robust procedure that consisted in "measuring the total amount in magnitudes that the light curve decays from its peak brightness during some specified period following maximum light." It was defined as the decline in the B -magnitude light curve from maximum light to the magnitude 15 days after B -maximum, a parameter he called Δ Δ m 15 . The lead sentence of the acknowledgments section of Phillips' paper states: "I am indebted to George Jacoby for suggesting the Δ Δ m 15 parameter as an alternative to Pskovskii's β." The relation states that the maximum intrinsic B-band magnitude is given by