Replying to True center?

Is it more accurate to measure center by going from the tip and holding the tape along the topsheet to the middle and then from the tail along the topsheet to the middle

Or

From the tip straight across in a sort of triangle to the middle and then from the tail in a triangle straight across to the same spot in the middle not accounting for the shape of the skis topsheet

Is it different for symetrical and non symetrical skis?

Does it make any difference at all?

Only answers from people who actually know what they're talking about please