Testing of engine particulate matter production during a transient is made more accurate by selecting an appropriate sized opening for a test probe of the sampling system located in the exhaust line upstream from a particulate trap. Sliding members fitted for follower allow the fulcrum to slide with ease up and down, within the follower wherein the movement of the follower is stabilized by attaching members, which fasten the follower to the piston, such that the follower and piston move in unison, as a unit, within the cylinder. A two-stage switch network having fine stage switches and coarse stage switches connects the resistor taps to an output node of the PGA.