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Learn how to position objects with precision and measure using rulers and the Ruler tool. The rulers are helpful for positioning objects and the Ruler tool lets you precisely measure the length of objects.

Rulers

Rulers is an important but often overlooked tool in Photoshop. With rulers, you can position objects with expert precision. The rulers are located on the top and left side of the document window. If you don't see rulers, you can enable them by choosing View > Rulers.

Changing the zero origin

You can position the ruler to start from anywhere in the image that you want. To do this, click and hold on the top left corner of the ruler and drag. Position the cross hair where you want the ruler to start. In the image below, the ruler's zero origin was set to the edge of the pie chart. Notice now that the ruler starts from the area that you positioned the cross hair. In the image below, the ruler's zero points has moved from the top left to an inch away from the top left.

Specifying the units of measurement

you created a new document. For example, when you create a new document and you specify the image dimension in inches, the ruler's measurement unit will be inches. You can change this to any measurement that you desire.

To specify the units of measurement, right mouse click on the ruler and choose the measurement unit that you would like to use.

You can also set the units of measurement more precisely with the preferences tool. Choose Edit > Preferences > Units & Rulers. You only have to edit the Units and Point/Pica Size options. In the Units options, select the measurement unit that you would like to use. In the Point/Pica Size options, choose one of the following:

• PostScript (72 points/inch) if you will be printing the image on a PostScript device. Most modern printers use this option.
• Traditional (72.27 points/inch) if you will be printing on a traditional device that does not support PostScript.

The Ruler tool

In Photoshop CS3, you can use the Ruler tool that will help you further with positioning objects. It calculates the distance between two points. You can access the ruler from the toolbar as shown in the image below.

To begin, select the Ruler tool then drag from the point where you want to start to the end point. For example, in the image below, I drew a line from the top left edge of the rim to the opposite edge. You can hold down the Shift key while creating the measurement line if you want the line to constrain to a horizontal, vertical, or 45º angle. If you make a mistake, you can click and drag on one of the two ends of the measurement line.

After you created a measurement line, you can see the measurement data in the option bar near the top of the Photoshop interface. Make sure that you have the Ruler tool selected or else you won't see this data there.

Snapping

Snapping can help speed things up and increase accuracy when using tools such as the Ruler tool. Snapping snaps your mouse to the edge of objects when your mouse is near the edge. To enable or disable snapping, choose View  >Snap. Then, choose View > Snap to to edit the snapping options.

Snapping is something that you will be enabling or disabling often because it can sometimes be helpful or annoying. For example, snapping can help you create a measurement line quicker and more precisely by automatically snapping to objects edges. However, when you want to create a point near an edge, but not exactly on it, the snapping may make it impossible to do. To disable snapping, you can choose View > Snap or, easier, hold down the Ctrl key.