This tweet made me scratch my head, it seems so counter intuitive:

If you create a little waterfall, you can see the effect better. In both cases, the delta is half the size of the bigger column.

Yes, using logarithmic scales would be the correct mathematically thing to do, but they are very hard for people other than mathematicians to get their head around. 

Read an earlier blog post about constructing waterfall charts in presentations. Cover image by Ross Findon on Unsplash