Sorry to resurrect this ancient thread... but... even while using un-cached data (i.e. always clicking the ! triangle) I still get weird results. For example, I select a rectanglar area, and tell it to only consider pixels in the selected layer. That gives me a number (like 70003). Then with the magic wand I subtract from the selection all the empty space in that same layer, and the same measurement becomes 59515. The selected pixels should be all and only the pixels present in that layer (or part thereof), so how it is possible that I always get different numbers?

Thanks.