Constants in proportional formulas are essential for maintaining consistency across different unit systems, allowing for accurate comparisons of physical quantities. When two variables are proportional, their ratio remains constant, represented by the equation y = kx, where k is the constant. This constant ensures that equations, such as the gravitational force equation F = GMm/r^2, yield results in standard units, facilitating comparisons with other forces. The discussion also touches on the concept of "natural units," which can eliminate these constants but may complicate comparisons across different physical properties. Understanding the role of constants is crucial for clarity and accuracy in scientific equations.