HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

EN Vertical Motion Index (VMI) Command 5-23
Common VMI Settings
To print 66 lines per page on letter-size paper, in portrait orientation
(with one-half inch top and bottom margins) send:
?&l7.27C 7.27 = (10/66) x 48
To print 66 lines per page on letter or legal-size paper, in landscape
orientation (with one-half inch top and bottom margins) send:
?&l5.45C 5.45 = (7.5/66) x 48