Continuity says A * v stays constant along a pipe, so narrowing the cross-section forces the fluid to speed up to keep the same flow rate, mass conservation for an incompressible stream. The trend is exact only for stated area and speed in the steady incompressible flow model. Real fluids add viscosity, turbulence, compressibility, pipe losses, geometry tolerance, calibration, and measurement uncertainty.
Two sections keep the same checked flow rate. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.