A fixed heat flux crosses a two-layer stack. Inside each layer the temperature falls as a smooth ramp set by that layer’s conductivity; at the seam it steps down by ΔT = R″q. Drag the interface conductance across its three-decade range and watch the step grow from invisible to dominant; the chips report the boundary’s share of the total temperature budget and the “equivalent thickness” of material it impersonates.
One-dimensional series teaching model: two equal layers of a 100 W/mK reference material with adjustable thickness, constant properties, ideal flux. Real stacks add spreading, anisotropy and temperature dependence; the staircase and its arithmetic survive.