We have this concept in aikido that I call a "measuring stick." That is, some aspect of how we practice that we use to objectively determine the rightness of our position. One of the first and simplest examples of a measuring stick is our practice of always measuring ma-ai before each repetition of a technique (except in kata mode). This allows us to better ingrain this distance in our mind. Similarly, at the end of hanasu#1, I have my students place a ki hand on uke's elbow in order to demonstrate that they are in the right place (shikaku) behind uke. These measuring sticks pop up a lot in our practice as little checks to give our subconscious mind more information for the learning process.
A very important instance of a measuring stick is the standardized step in tegatana. The purpose of tegatana is to calibrate our most basic measuring stick - the step. If every step we ever take is some random length then we have no way of using a standard step as a measuring stick. So, in tegatana we consciously work on creating a constant, atomic-level, discrete step length. The step is bounded by something objective (our hip width) and can therefore be used throughout the rest of aikido to tell the subconscious mind whether or not we're in a familiar relationship.
Of course, most of the time tori will have to extend or shorten his steps as dictated by uke, but whenever toris steps approach that calibrated measuring stick step then his subconscious is automatically in familiar territory. The measuring stick steps help tori to remove some of the perception of chaos from the system. So, in our practice of tegatana we want to make sure to standardize those steps to hip width and begin every single class with at least one run-through of tegatana as a calibration of our measuring sticks.
There are other measuring sticks in tegatana, including our practice of always keeping both hands within our peripheral vision and always ending hand and foot motions at the same time. Perhaps those can be topics for another day.