The impedance value is added to {HEAD ~ a series connected resistor} to provide {TAIL ~ the output impedance} 
to provide
The impedance value is added to { HEAD ~ a series connected resistor } to provide { TAIL ~ the output impedance }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL