Hi Martin, yes like Pilou mentions the dimensions that are shown at the top level are done more quickly - for solids they're based off of the display mesh and for curves they're based off of a number of sampled points.

Because that size readout is updated very frequently with every selection change, it has to be calculated quickly and it would not work very well to have a lot of delays for the more intensive and accurate calculation on every selection change.

When you pop open the menu, it does the more accurate calculation at that time for the result that is shown in the menu.

- Michael