Someone asked me to clarify how the various blurs compare as you do focus stacking with the Focus Bar.
This chart shows the relationship between two images taken at different focus distances, #1 and #2.
The first image (#1), as well as the second one (#2), shows the meaning of the cyan bar. That is the area of defocus where the defocus blur is less that the sensor limit of twice the sensor's pixel pitch.
The magenta bar that shows on the second image tells you where the depth of field overlaps with the first image's depth of field.
Finally, the overlap blur value, which the Focus Bar reports, is where the depths of field of the two images cross each other. It is this value that you should use to ensure high quality focus overlaps. For example, if this value was about the defocus limit, you would just have an overlap. If this value was zero, you would have a full overlap, ie one image on top of the other. Overlap values less than the sensor limit (twice the pixel pitch) are rather meaningless.
Bottom line: you have all the information you need to make perfect focus stacks.