One situation in which measurements have an unlimited number of significant figures is when we are defining a conversion factor between two different units. For example, when we define that 2.54 cm is equal to 1 inch, we are essentially saying that there is a precise relationship between these two units. In this case, we can say that the number of significant figures is unlimited because the relationship between the two units is exact. Similarly, when we define that 12 inches is equal to 1 foot, we are again establishing a precise conversion factor with an unlimited number of significant figures.
