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750: Mainline

Next, suppose that you decide to install a Decrement button. You first click the button on the left side showing the OK-button icon, the one under the button labeled A.

Then, a new set of buttons appears in the adjacent column. You click the OK-button icon in that adjacent column, indicating that you want a labeled button.

At this point, you move the cursor inside the application window, which is now titled Meter Demonstration. A click, drag, and release produces a button.

You proceed to replace Button in the Text field with your preferred label, Decrement.

Next, you move to the When: list box and the Perform: text field. You select the clicked option from the list box, and type decrementMeter, without a colon, in the text field. By so doing, you indicate that you will supply a callback method named decrementMeter:, with a colon, for the clicked event associated with the button.

As soon as you supply the method name, an asterisk appears in front of clicked, which indicates that a callback method name has been supplied.

All this work leads to the following display: