Here’s another, brief, post on the subject of dimensional analysis; it concerns a curious interpretation of dimensions. [Previous posts concerned statistics and kinematics.]

Consider cars. A typical fuel efficiency is

≈ 40 mpg (miles / gallon [UK])

≈ 14 km / litre = 14 m / cc = 14 mm / mm^{3}

Expressed differently (taking the reciprocal), this is about

≈ 4 fl oz [UK] / mi

≈ 70 ml / km = 70 cc / km = 70 mm^{3} / m

≈ 70,000 μ^{2} = 70,000 μm^{2} = 0.07 mm^{2}

What’s that? It’s a unit of area.

If you imagine forming a tube of fuel as the car uses it (as the car goes along), then that’s the tube’s cross-sectional area.