How far away is the nearest galaxy to the Milky Way? How long is the distance from Boston to New York? How deep is the Marianas Trench? How high is the tallest building? How many marbles are in that bag? The above questions all require measuring quantities to arrive at an answer. Measuring the number of light-years from the Milky Way to the other galaxies in the local group will reveal which is closest. Measuring the number of miles from Boston to New York will reveal the distance between them. The Marianas Trench will contain a measurable number of feet that will be its depth. The tallest building will contain a measurable number of feet that will be its height. Counting the marbles will yield the quantity of marbles contained in the bag. While the units of measure of quantities and methods of obtaining measurements vary, all measurable quantities have one thing in common; they can all be expressed as real numbers.