Hold down the Shift key to alter the behavior of the following commands and tools as indicated.

Image>Adjust>Brightness/Contrast tool: Simultaneously adjust all channels of a composite image
Image>Adjust>Threshold: Adjusting Min also adjusts Max
Image>Zoom>In: Do not enlarge window
Analyze>Histogram: Display log histogram
Analyze>Tools>Roi Manager (“Add”): Draw and add selection
Macros in Plugin menu: Open instead of run
Rectangle and Oval selection tools: Force selection to be square
Area selection tool: Add this selection to previous one
Polygon selection tool: Shift-click on a node to duplicate it
Segmented line selection tool: Shift-click on a node to duplicate it
Point selection tool: Shift-click to add a point
Zoom tool: Shift down, then click and drag to zoom to the selection