Time dependence of cell voltage V_c (product C10F3 with a cell thickness of 5 μm and a current square signal of ±5 nA). The slope of the linear part at the beginning of the rise allows a measurement of ε_eff in the unrolled SmC* phase. The measurements of Δt and ΔV_c on both unspecified points (A and B) make it possible to determine ΔP. Colored lines represent the square current signal.