1. A method for measuring at least one property of a web of material as said web is being manufactured and is moving in a machine direction (MD) by scanning measurement apparatus back and forth across said web in a cross-machine direction (CD), said measuring apparatus comprising a source of radiation appropriate for measuring said at least one property that is directed toward said web and at least first and second sensors that receive measuring radiation from said web, said method comprising: receiving radiation representative of said at least one property of said web at consecutive points across said web; measuring temperature at said consecutive points across said web; interrupting said measuring radiation at an edge of said web; sensing radiation at said edge of said web while said measuring radiation is interrupted; measuring temperature of said edge of said web; developing correction factors for said at least one property from said web edge temperature and the measured temperatures of said consecutive points for each of said consecutive points across said web; and applying said correction factors at each of said consecutive points across said web to correct for Planckian radiation contained in radiation representative of said at least one property of said web received at said consecutive points across said web.