IBM 6400 Setup Manual page 273

During each sweep of the shuttle, hammers are activated to print dots at the
required positions in the dot row. When the shuttle reaches the end of a
sweep, it reverses direction, and the paper advances one dot row. The
hammers print the next row of dots as the shuttle sweeps in the opposite
direction, as shown in Figure B–2, unless unidirectional printing is chosen.
After a line of characters is printed, the paper advances to the first dot row of
the next print line. This creates a number of blank rows between lines of
characters, depending on the print mode and line spacing you selected.
Dot
Start
Row
1
2
3
4
5
6
Character
7
Line
8
*
9
* *
10
Space
11
12
1
2
* Used for lowercase descender only
* * Used for underline and lowercase descender
Direction of shuttle movement
1 Hammer
Print Span
Figure B–2. Line Matrix Printing
Appendix B. A Quick Look at Line Matrix Printing
Paper
Advances
Paper
Advances
1 Hammer
Print Span
Paper
Feed
B–3