Supposing a table's width and length are measured a number of times using a ruler with a certain resolution. A manufacturer provides the theoretical values for both length and width. Thus we may calculate the practical and theoretical values of the table's area (S). How may Nσ for the area of the table S be calculated, given that Nσ = |X1 - X2|/SQRT(σ1^2 + σ2^2)? Will it be correct to say that Nσ equals |S practical - S theoretical|/SQRT[(σ of S practical)^2 + (σ of S theoretical)^2]?