Prior to the sentencing guidelines, Federal parole guidelines determined the seriousness of a drug trafficking offense by three factors: the nature of the controlled substance, the weight of the mixture containing that controlled substance, and the purity of the controlled substance in relation to the mixture in which it was contained. Early proposed sentencing guidelines also used this method to determine the seriousness of drug trafficking offenses. Midway through the period of the U.S. Sentencing Commission's development of the initial sentencing guidelines, Congress enacted the Anti-Drug Abuse Act of 1986. In this act Congress specified a number of mandatory minimum sentencing provisions that restricted the commission's discretion in the development of guidelines for drug trafficking offenses. The commission, which had not yet promulgated its initial guidelines, responded to this legislation by adopting it 5-year and 10-year mandatory minimum sentences, as well as the controlled substances and quantities associated with these mandatory minimum sentences, as reference points for the development of its drug trafficking offense guideline. The offense guideline was expanded upward and downward in two-level increments to address trafficking in larger and smaller quantities of the controlled substances listed in 21 U.S. C. Section 841(b)(1)(A) and 841(b)(1)(B). Within this framework, the commission then assigned offense levels for controlled substances not specifically listed in the United States Code. Using the weight of the entire mixture containing a detectable amount of the controlled substance, rather than the weight of the controlled substance itself, was a departure from the past practice of the Parole Commission, but the Sentencing Commission believed this was required to bring the guidelines in compliance with the provisions of the Anti-Drug Abuse Act of 1986. The commission expects that continuing research, experience, and analysis will result in revisions to the guidelines by submission of amendments to Congress. 29 footnotes