IBM 6400 Setup Manual page 201

The following table lists the maximum number of characters that can
be printed for a given Characters Per Inch (CPI) setting.
CPI Setting
10.0
12.0
13.3
15.0
16.7
17.1
18.0
20.0
* = Default
If the forms width is set in characters and the CPI is changed, the
effective page width is changed to be equal to the forms width in
characters divided by the new CPI. For example, if the current forms
width is 132 characters and the CPI is changed from 10 CPI to 15 CPI,
the effective forms width changes from 13.2 inches to 8.8 inches.
NOTE: This applies only if the forms width is set in characters. If the forms
width is set in inches or millimeters (mm), changing the CPI does
not affect the effective forms width.
Maximum Forms Width
(in Characters)
* 136
163
181
204
227
232
245
272
IMPORTANT
Chapter 4. Configuration Menus 4–85