Measure the width inside the window opening. Measure the height inside the window opening. Do not make any deduction. Never measure existing blinds. Double check your measurements. Record string position. REASON FOR CHOOSING INSIDE MOUNT Clean Look Inside-mount treatments are installed inside the window casing, showcasing attractive window trim. The window opening frames the treatment for a finished, clean appearance Allow Sill Space on Deep Windows In some deep-set windows, window treatment can be installed to allow plants or other items to be placed in front of the window on the sill. LIMITATION OF THE INSIDE MOUNT Light Gaps A small reduction in the width and/or length is taken at the manufacturer to allow for proper operating clearance, and this causes a small gap on each side of the window treatment, affecting the window treatment’s ability to darken a room. Obstructed View The stack (a compressed portion of the window treatment when fully raised) will obstruct part of the view from the window. The amount of stack varies by product. Architectural Obstacles Obstacles such as handles and cranks can interfere with the operation of Inside-mount treatments.