A base for supporting posts of fencing, which base includes a block of plastics provided with apertures for receiving the ends of fencing posts. Means for Solution In a sensor control apparatus, before drive control is started, preliminary control is executed so as to supply a constant current to a second oxygen pump cell over a constant time, to thereby control to a constant level the amount of oxygen pumped from a second measurement chamber to the outside of the second measurement chamber. For example, in one embodiment a front ferrule and a back ferrule for a tube fitting may be snapped together.