Horizontal guides are horizontal lines that act as:
•Y coordinate snap points when adding or moving objects.
A horizontal guide (blue line)
There are 2 ways to add a horizontal guide to a sheet.
2.The second method is to click on the button in the Add→Guides button group.
The horizontal guide and its horizontal position during initial creation
In both cases, as you drag the guide to position it you can enter a number value by first pressing the Enter key and then the Y coordinate or click the left mouse button to place the guide.
You can press the 's' key at any time to turn snap on or off.
There are 2 ways to edit a horizontal guide, dragging it or using the Properties panel.
You can hold down the left mouse button on a horizontal guide and drag the mouse to move the guide. You will see the Y value of the coordinate change as you move it. Press the 's' key to turn snap on or off.
Horizontal guide's vertical position displayed during dragging
If you select a horizontal guide and the Properties panel is visible, the horizontal guide properties dialog will be shown.
Horizontal guide properties
The Y or vertical position of the horizontal guide
Pressing the button displays this help page.