In this article, the author believes that a visual image of the number system is helpful to everyone, especially children, in understanding what is, after all, an abstract idea. The simplest model is the number line, a row of equally spaced numbers, starting at zero. This illustrates the continuous progression of the natural numbers, moving to the right as the values increase and their indefinite extendibility. There are three models of the decimal number system discussed in this article--the "Decimal Helical Number Line" or a "Numdrum," the number line, and the number square. The number line enables simple counting on (addition) and back (subtraction). As numbers approach 100, the length of the number line becomes unwieldy and inconvenient in the classroom. The next step in developing a model of the number system was the arrival some years ago of the number square. This was an attempt to make the number system more compact, more versatile and more interesting. It succeeded, but only up to a point. The idea is to cut the horizontal number line into lengths of 10 digits, then to arrange the rows of numbers in a square grid formation, starting with the smaller numbers at the top, with the values increasing as the rows progressed downwards. A variation of the horizontal number line is the vertical number line, which has a familiar appearance (thermometers, floors in a tall building, etc) and creates a link between number value and height. In this article, the author says that the "decimal helical number line" has advantages over conventional number lines and number squares. (Contains 3 figures and 2 notes.)