Keep the moving panel in the closed position, and place the Measuring Tool (B) with the short edge touching the SmartSlydr as show in the picture to mark the bottom edge.
Similarly Open the moving panel and mark the bottom edge.
Ideally both marking should be the same or less than 1 cm (3/8 inch).
In less likely situation where the distance between the two markings is greater than 1 cm (3/8 inch), leveling is required. This can be done by placing padding between the brackets.