Constant of Proportionality

When scientists or theoreticians find a mathematical relationship between two quantities, they design an equation, so that, for example, if one quantity is known, the other can be solved for. However when a scientist wants to solve for a quantity, they have to make sure that the units work. A constant of proportionality is a number that is inserted in to the equation which performs this task.

For example, if you knew that force x distance was proportional to work, but you wanted a concrete equation, you could say force x distance equals a constant times work. The constant is the constant of proportionality. You could find it by plugging observed data into the equation and solving for it.