&quot;When scientists measure any quantity they must specify the units being used.&quot;<p>No they don&#x27;t. For instance, a simple aspect ratio measures how something is wide relative to how it is long. It has no units.<p>This here desk I have here is about 1.7 times as long as it is wide. No inches or centimeters required.<p>There isn&#x27;t anything amazing or mystical about a unitless quantity.