Roller Insect Screens - Measuring a Window with a Top Opening Pane

If you are ordering a roller insect screen to install at a window that is made up of a top opening pane above a fixed pane, then you may not need to cover the whole window with a fly screen. Instead, you can cover just the top opening pane. 

Why cover only the top opening pane?

This has cost advantages because you only need to order a screen to cover part of the overall window - so the screen should be smaller and lower cost.

Why cover the whole window?

Covering only one panel, rather than the whole window, usually requires the screen to be fixed to the window frame itself. If you wish to avoid fixing directly to the window frame. Then you may still wish to order a screen to cover the full window and side/top fix the screen into the recess.