In Photoshop the same effect can often be achieved in a number of ways. Interface setup is no exception. If you are accustomed to working with the menu bar, select "View" and set the dropdown marker next to the item "Line".
If you prefer working with hot keys and did not change the program settings by default, press Ctrl and R. the Line is displayed on two axes: X and Y, that is, width and height of the window.
In accordance with the predefined parameters, the unit appeared line are inches, but you can change the settings, select inches, millimeters, pixels, or percent. To set the desired units, click the right mouse button anywhere on the line, open the drop-down menu. Select the desired item by clicking on it with the left mouse button.
In addition to the line, as part of the user interface in Adobe Photoshop is a tool of the same name. It helps to accurately set the coordinates of the initial point, calculate the length and width of the fragment to determine the angle. This tool, you can choose either to panel or to call by pressing hotkeys.
To select the Ruler tool, make sure that the editor window displays the "Toolbar", move the cursor to the eyedropper tool and click on the icon of the button with the little triangle. Unfold the submenu. Select with the tool "Line".
To invoke the "Line" tool hotkeys, press and hold Shift, then press I to until icon "Pipette" in the selected tools icon appears in the Line.