Provided in the kit is a template that will help determine the length of the regulator. Towards the bottom of the template is a printed line, which marks where the bottom of the glass will sit when placed in the window channel on the regulator. I placed that line at the bottom of the Brothers glass and then marked the top of the glass on the template. From there I transferred that template to the door, as if the glass’ upper edge was in the down position at the doorsill. I then marked the door per the dimensions of the template. This will also help determine where to place the regulator mounts.