IBM 6400 Setup Manual page 75

To avoid damage to the printer caused by printing on the platen, always
align the edge of the left tractor door with the number "1" on the paper
scale.
Tractor Splined Shaft
Horizontal
Adjustment
Knob
Newer 6400 Series Models
Figure 52. Using the Paper Scale as a Guide
10. If adjustment is necessary:
a. Unlock the left tractor.
b. Slide the tractor until it is directly to the left of the number "1" on the
11. For the older 6400 Series models:
After both tractors are secured, use the horizontal adjustment knob to
make fine horizontal paper adjustments.
ATTENTION
Tractor
Paper Scale
Tractor Splined Shaft
paper scale and lock it. You can also use the paper scale to count
columns.
Setting Rear Paper Exit
Older 6400 Series Models
Tractor
Paper Scale
Paper
75