Cover plate with length compensation

A method of dosing an installation duct carrying a supply line, comprising:

• providing a first cover plate with a first cover plate first front side and a first cover plate second front side and a surface facing the installation duct, said first cover plate having a shoulder-like recess with a recess height, said recess extending approximately rectangularly into said first cover plate, said first cover plate including a functional component connectable to the supply line;
• providing a second cover plate with a second cover plate first front side and a second cover plate second front side, said second cover plate including a functional component connectable to the supply line, said second cover plate second front side being directed toward said first cover plate first front side, said second cover plate second front side having a portion with a height substantially corresponding to said height of said recess of said first cover plate, said second cover plate second front side extending into said recess such that said first cover plate and said second cover plate together extend a length;
• and
• adjusting a degree of overlap between said first front side of said first cover plate and said second front side of said second cover plate to change said length of said combined cover plates.