The total cross section should not depend on the renormalization and factorization scale.
This mean that a cross-section computed at NkLO order in perturbation theory should depend on the scales only at Nk+1LO.
Hence it is possible to assess the impact of the neglected terms by studying how much the cross-section changes when varying the scales.
The scales are varied around the reference scale (RS).
The two possible choices "standard" and "conservative"
correspond respectively in varying the ren/fact scales in the square
[1/2 RS, 2 RS]x[1/2 RS, 2 RS] (9 points)
and in the square
[1/4 RS, 4 RS]x[1/4 RS, 4 RS] (25 points).