Symmetric Pattern 2; Symmetric Pattern 3 - Epson FX Series User Manual

Here's another interesting variation:
20 MAX=64: MIN=l: RE=l: N=1/2
40
N=N*2
70 N=N/2
Quite a difference! Instead of adding and subtracting one from N,
lines 40 and 70 now double and halve it. This geometric progression
creates a very different pattern.
196
Figure 14-5. Symmetric pattern 2
Figure 74-6. Symmetric pattern 3