GETTING A FRESH HISTOGRAM IN ONE CLICK

When you have the Histogram palette open to monitor your tonal adjustments to an image, you may see a tiny warning symbol in the right corner of your histogram. That's its way of letting you know that you're looking at a Histogram reading from the Histogram's memory cachenot a fresh reading. If you want to refresh the Histogram and get a new reading (and you should), you can click directly on the tiny warning symbol and it will refresh immediately for you.