About: http://webisa.webdatacommons.org/417494065

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	In the manufacture of multifocal lens blanks, a conventional glass blank made of a white or photochromic glass is machined to form a recess at a position where s segment of different power is needed in the lens e.g. for reading.
http://www.w3.org/ns/prov#wasQuotedFrom	google.com