If three components are to be conveyed in three separate channels with identical unity excursions, then the Pb and Pr colour difference components are used. These scale factors limit the excursion of EACH colour difference component to –0.5 … +0.5 with respect to unity Y excursion: 0.886 is just unity less the luma coefficient of blue. In the analogue domain, Y is usually 0 mV (black) to 700 mV (white), and Pb and Pr are usually ±350 mV. YPbPr is part of the CCIR Rec. 709 HDTV standard, although different luma coefficients are used, and it is denoted E'Pb and E'Pr with subscript arrangement too complicated to be written here. YPbPr is employed by component analogue video equipment such as M-II and Betacam; Pb and Pr bandwidth is half that of luma. A version of the (Y, R-Y, B-Y) signals specified for the SMPTE analogue component standard.