To help people decide what drop-down list option to select, and even to let them know that a cell contains a drop-down list, you can create a message that appears when they select a cell. Or that shows an error message when a drop-down list option isn't selected properly.
Create input and error messages
To help people decide what drop-down list option to select, and even to let them know that a cell contains a drop-down list, you can create a message that appears when they select a cell. You can add the message to all cells that contain the drop-down list, or just the first cell in a column.
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Select the cells that you want to create a message for, and click Data Validation.
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On the Input Message tab, check the box next to Show input message when cell is selected.
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Type a Title if you want. It’ll appear in bold.
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Type the message in the Input message box. Now, when you click a cell, the message pops up.