Changing criterion designs (CCD) are single-case experimental designs that entail a step-by-step approximation of the final level desired for a target behavior. Following a recent review on the desirable methodological features of CCDs, the current text focuses on an analytical challenge: the definition of an objective rule for assessing the correspondence between criterion levels and behavior. We review extensively applied research and methodological recommendations for establishing experimental control, such as the range-bound CCD, and integrate them into a proposal for a formal expression of an objective rule. We illustrate how this proposal can lead to establishing the acceptable level of behavior prior to gathering the intervention phase data and how it leaves space for professional judgment. A discussion of software implementing the suggested proposal is included.