.NHPoint Sizes; Line Spacing.PPAs mentioned above,the command.BD .pssets the point size.One point is 1/72 inch,so 6-point characters are at most 1/12 inch high,and 36-point characters are \(12 inch.There are 15 point sizes, listed below..P1 1.ps 66 point: Pack my box with five dozen liquor jugs..ps 7.vs 8p7 point: Pack my box with five dozen liquor jugs..vs 9p.ps 88 point: Pack my box with five dozen liquor jugs..vs 10p.ps 99 point: Pack my box with five dozen liquor jugs..vs 11p.ps 1010 point: Pack my box with five dozen liquor.vs 12p.ps 1111 point: Pack my box with five dozen .vs 14p.ps 1212 point: Pack my box with five dozen.vs 16p.ps 1414 point: Pack my box with five.vs 24p\s1616 point\s18 18 point\s20 20 point.vs 40p\s2222\s24 24\s28 28\s36 36.ps 10.vs 12p.P2.PPIf the number after.BD .ps is not one of theselegal sizes,it is rounded up to the next valid value,with a maximum of 36.If no number follows.BD .ps ,.UL troffreverts to the previous size, whatever it was..UL troffbegins with point size 10,which is usually fine.This document is in 9 point..PPThe point size can also be changed in the middle of a lineor even a wordwith the in-line command.BD \es .To produce.P1\s8UNIX\s10 runs on a \s8PDP-\s1011/45.P2type.P1\es8UNIX\es10 runs on a \es8PDP-\es1011/45.P2As above,.BD \es should be followed by a legal point size,except that.BD \es0 causes the size to revert toits previous value.Notice that.BD \es1011can be understood correctly as `size 10, followed by an 11', if the size is legal,but not otherwise.Be cautious with similar constructions..PPRelative size changes are also legal and useful:.P1\es\-2UNIX\es+2.P2temporarily decreases the size, whatever it is, by two points, thenrestores it.Relative size changes have the advantage that the size differenceis independent of the starting size of the document.The amount of the relative change is restrictedto a single digit..WS.PPThe other parameter that determines what the type looks likeis the spacing between lines,which is set independently of the point size.Vertical spacing is measured from the bottom of one line tothe bottom of the next.The command to control vertical spacing is.BD .vs .For running text, it is usually best to set the vertical spacingabout 20% bigger than the character size.For example, so far in this document, we have used``9 on 11'', that is,.P1^ps 9^vs 11p.P2If we changed to.P1^ps 9^vs 9p.P2.vs 9p.ne 3the running text would look like this.After a few lines, you will agree it looks a little cramped.The right vertical spacing is partly a matter of taste, depending on howmuch text you want to squeeze into a given space,and partly a matter of traditional printing style.By default,.UL troffuses 10 on 12..PP.vs 14p.ps 12Point size and vertical spacing make a substantial difference in the amount of textper square inch.This is 12 on 14..ne 2.PP.ne 2.ps 6.vs 7pPoint size and vertical spacing make a substantial difference in the amount of textper square inch.For example,10 on 12 uses about twice as much space as 7 on 8.This is 6 on 7, which is even smaller.It packs a lot more words per line,but you can go blind trying to read it..PPWhen used without arguments,.BD .psand.BD .vsrevert to the previous size and vertical spacingrespectively..WS.PPThe command.BD .spis used to get extra vertical space.Unadorned, it gives you one extra blank line (one.BD .vs ,whatever that has been set to).Typically, that's more or less than you want,so.BD .spcan be followed byinformation about how much space you want _.P1^sp 2i.P2means `two inches of vertical space'..P1^sp 2p.P2means `two points of vertical space';and.P1^sp 2.P2means `two vertical spaces' _ two of whatever.BD .vsis set to(this can also be made explicit with.BD .sp\ 2v );.UL troffalso understands decimal fractions in most places,so.P1^sp 1.5i.P2is a space of 1.5 inches.These same scale factors can be used after.BD .vsto define line spacing, and in fact after most commandsthat deal with physical dimensions..PPIt should be noted that all size numbers are converted internallyto `machine units', which are 1/432 inch(1/6 point).For most purposes, this is enough resolutionthat you don't have to worry about the accuracy of the representation.The situation is not quite so good vertically,where resolution is 1/144 inch(1/2 point).