Calculus is how you measure
things that keep changing.

A ruler tells you where the water is. Not how fast it is rising, or how much has come in. No single reading can. Calculus does.

d means a tiny bit of. ∫ is a stretched S: Sum.

dy/dt tiny rise ÷ tiny time. The arrow.

∫ dy every tiny rise, added up. The water.

Everything below is drawn on this tank. Seven of them are ★ core topics. Understand those, and the other 56 follow from them. Scroll.