It will be appreciated that by zero power or plano, it is meant that {TAIL ~ the optics} provide {HEAD ~ no substantial visually discernable correction} to the human eye 
It will be appreciated that by zero power or plano , it is meant that { TAIL ~ the optics } provide { HEAD ~ no substantial visually discernable correction } to the human eye
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH