Adjusting screen size / percent image size should be added to the end user toolbar.
Adjusting screen size / percent image size should be added to the end user toolbar, as well as the "undo" button, and the "re-do" button.
Are the YAHOO software developers reading these recommendations ?
The zoom setting is controlled by your web browser. Most browsers will indicate what percent zoom you are up in the address bar.
You can user the keyboard commands to Undo/Redo typing, CTRL+Z and CTRL+Y, respectively, depending on your device.