The window glass is usually covered, at least partially, when you have an inside mount with vertical blinds. When measuring for an inside mount you need to measure the exact width of the window opening across where the headrail will be installed. Correctly measure from the inside trim on one side to the inside trim on the other and round the measurement down to the nearest 1/8”. Now, measure the exact height of the window from the inside trim to the top of the windowsill or the exact length you would like your blinds to hang. Next, measure the height in three places (left side, center and right side). Then measure the depth of your window frame. You can only use the “available” depth, which does not include inside trim, window cranks or tracks. Only include space that is available for installing mounting brackets. When choosing your vertical blind you will have to consider the minimum depth required to have a inside mount, so it will fit properly and not stick out of the window opening.