I need to make a precise white balance selection. How accurate is the White Balance picker cursor?
The White Balance cursor has a single-pixel sample size for the zoom level. That is, at 100% zoom, the sample will be taken from one pixel in the source file.
When at another zoom level, the cursor still samples at the single point of the preview, however as the zoom involves some down-sampling, the sample will reflect this averaging. Here is the same process at 33% zoom in the viewer: