Vertical Imbalance at the reading level, continued.

We are still concerned with how much correction we will need for the glasses wearer to be able to read without diplopia.  We may correct the problem with slab-off, or with one of the other options.  We may discover that there is no remaining vertical imbalance problem.

When we computed vertical imbalance at the reading level before the two lenses had the same ADD, so we could ignore the prism induced by the segment.   (We could ignore it because each segment would be providing the same amount and base direction of prism, so they would cancel each other.)
sagittal cut of plus Rx with different adds

Now we have the segments inducing different amounts of prism, so we need to include this amount in our calculations.

The glasses pictured here might have the following Rx:

OD +5.00 sph,  ADD +3.00
OS +2.00 sph,  ADD +1.00