Rulers and Guides

Rulers and guides in Fireworks can be very useful when you want move, resize and modify elements to particular dimensions.

Choose View > Rulers
If Rulers has a tick beside it in the menu then they are visible. If it does not selecting Rulers in the menu will make the rulers visible.
Click and drag from within the ruler at the left-hand side of the page to create a guide.
Drag a horizontal guide down from the top ruler and position it at 400 pixels down.
You will read this from the vertical ruler.
You can choose to show or hide guides as you are working. To do this choose View > Guides > Show Guides.
If there is a tick beside Show Guides then they are visible. To hide them simply click on Show Guides to make them visible click on Show Guides in the menu again. This is called toggling a menu item.