Final answer:
The question seems to request a comparison or conversion between 15 and 18 yards; however, as both are in the same unit, the International System of Units standardizes a yard as 0.9144 meters, ensuring consistency worldwide.
Step-by-step explanation:
The question '15 yards to 18 yards' appears to be asking for a conversion or comparison, but the units are the same, which indicates it may actually be looking for the difference between two measurements. Nonetheless, to address the question within the context of measurement, it's important to understand how long a yard is in the modern context.
In the International System of Units, a yard is clearly defined as a unit of length. Today, a yard is standardly accepted to be equal to 0.9144 meters, and this definition is consistent worldwide. This means that whether a football player moves the ball ten yards for a first down or if you were measuring fabric, one yard in Los Angeles will be the same as one yard in Dallas or Green Bay.
Historically, the yard had been arbitrarily defined, for example, as the distance from the tip of a king's nose to the end of his outstretched hand. However, this would cause issues with consistency especially when power changed hands. Now, with a standardized measurement, there is no confusion or need to 're-mark' areas when there is a change in leadership or locales.