Update README.md

README.md

@@ -123,6 +123,9 @@ axstereo.wiggle('sun_wiggle.gif')  # saves to file
 
 ## Advanced Usage
 
+### Parallel vs Cross-Eyed Viewing
+By default, the stereograms are set up for the "parallel" or "divergent" viewing method as described above. For "cross-eyed" viewing, initialize with a negative `ipd` parameter. An ipd (Inter-Pupilary Distance) of 65 millimeters is the default, so call `AxesStereo2D(ipd=-65)` for the default cross-eyed viewing.
+
 ### Working With Plots
 The figure and subplot axes can be accessed with the following:
 ```python
@@ -178,10 +181,7 @@ These are not [*auto*stereograms](https://en.wikipedia.org/wiki/Autostereogram),
 </a>
 </p>
 
-### Parallel vs Cross-Eyed Viewing
-By default, the stereograms are set up for the "parallel" or "divergent" viewing method as described above. For "cross-eyed" viewing, initialize with a negative `ipd` parameter. An ipd (Inter-Pupilary Distance) of 65 millimeters is the default, so call `AxesStereo2D(ipd=-65)` for the default cross-eyed viewing.
-
-### Derivation of Geometry
+## Derivation of Geometry
 Two eyes with separation `IPD` are looking at a point a distance `z` offset from a focal plane at distance `d`, resulting in view angle `θ`. If this point were projected back to the focal plane, it would be offset by `δ` from where it visually appears on that plane. This offset `δ` is used to displace each point in the stereogram for each eye based on its `z` value to achieve the stereoscopic effect. The `eye_balance` parameter allocates the total relative displacement of `2δ` between the two eyes.
 
 ```