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SINGLE INTEGRATION
The water line represents a 1-dimensional measurement. You're measuring the length along a single axis - like marking the water level on the side of a glass. This is the foundation of integration: accumulating values along one dimension.
∫ f(x) dx
━ SINGLE (1D) - LINEAR PATH
Water line on glass edge • Measures length • One variable integration
▢ DOUBLE (2D) - SURFACE AREA
Top view of water surface • Measures area • Two variable integration
▣ TRIPLE (3D) - VOLUMETRIC
Full water volume • Measures 3D space • Three variable integration