Center of Gravity
The flexible tape wil place the CG SLIGHTLY forward of where you intended. Usually less than 1/8 inch difference.
Since a sligtly forward CG is rarely (practically NEVER) gong to destroy a model... its not a problem.
Remember... Nose-heavy = slugginsh performance. Tail-heavy = broken airplane. Its easier to fix noseheavy's result after landing than tailheavy's result after impact