A term referring to the experiment Deming describes to illustrate the futility and damage of adjusting a stable process in reaction to each outcome to try to affect subsequent results as desired. There are four rules of the funnel, three of which amount to tampering and produce more variation than if the process were left alone [see chapter 11 in Deming's out of the crisis]. See "tampering". Or an experiment that demonstrates the effects of tampering. Marbles are dropped through a funnel in an attempt to hit a flat surfaced target below. The experiment shows that adjusting a stable process to compensate for an undesirable result or an extraordinarily good result will produce output that is worse than if the process had been left alone.