> Minor nitpick: it's a "dyad" that is a combination of two notes.

> An "interval" is the difference between two (or more) pitches. And just as you'd measure the space between your eyebrows using a ruler, you'd measure the interval between middle C and concert A using your ears.

How are you imagining that works? If you had three eyebrows, how much space would there be between them? Intervals are, by definition, the space between two points.