What N-up means
N-up shrinks several pages onto one sheet — two, four, six or nine — so you can print slides as handouts or proof a long document on fewer sheets. Pages run left to right, then top to bottom, each scaled to fit its cell and centred.
Mixed page sizes and rotation
Each page keeps its own proportions and is placed the way it appears on screen, so a landscape page or one stored rotated is not squashed or turned sideways. Pages of different sizes share a sheet without being stretched.
Readability
Nine to a sheet is very small. Four is the usual limit for readable body text on A4; six or nine suit slides and diagrams.