Abstract: Reference bores are selected in blade extender and one or more reference plates are provided at a height (h1; h2) from extender flange. A reference laser device is provided within reference bores which beam impinging on reference plates is in line with bore axis. A blade root bore is selected and a laser device is fitted therein such that a measuring laser beam impinging on plates is in line with axis of blade root bore. The measuring laser beam can be then assessed. A measuring tool is used having a first end to which laser devices can be attached or other devices such as a comparator, and a movable second end for being inserted within the corresponding bores with a tight fit.