rejected and provides the printing station 55 with information for marking the devices 10 where appropriate the controller may also control the composition of the conductive polymer material by regulating the control valves 23 of the supply bins 21 as each device 10 is cut from the continuous strip 100 its resistance is measured as the resistance of each device is in milliohms care must be taken with this measurement and fig3 illustrates a preferred way of taking this measurement probes 47 of a resistance measuring device 46 are brought into contact with respective terminals 12 of the device 10 each probe 47 has three fingers comprising gold or gold plated spring loaded spikes 48 to make point contact with the surface of the ptc device 10 the spikes are spring loaded to ensure a consistent probe pressure is applied to each device as probe pressure may influence the resistance reading in this way probe pressure will not be a factor causing variations in readings between devices produced in the same machine also each probe has three fingers to ensure good contact with the terminal surface and is not as susceptible to fluctuations due to surface contamination as a single contact point while the embodiment shown illustrates a printer preferably of the ink jet type printing indicia onto the devices after their resistance value has been measured this is purely an optional feature however an advantage of this optional feature is that each.