The necessity of the mathematical description of living processes and the recent advances in theoretical syntheses that fit surprisingly well with real data have led many scientists to experiment with new "generalizations," beginning with allometric equations. I present here, briefly, why caution is needed when allometric equations are multiplied or divided to make new ones. This practice is flawed by old and recognized problems, such as the fallacy of averages combined with misunderstandings that include error propagation, misuse of statistics and confounding scale.