{TAIL ~ The first unit} is connectable to a first voltage source and the second unit is connectable to {HEAD ~ a second voltage source} 
{ TAIL ~ The first unit } is connectable to a first voltage source and the second unit is connectable to { HEAD ~ a second voltage source }
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD