Table 4

	Mean difference	Range
Set Default	0.84% ± 0.15%	-3.63% to 8.43%
Set 1	1.08% ± 0.15%	-2.60% to 9.46%
Set 2	0.35% ± 0.32%	-6.63% to 6.66%
Set 3	0.21% ± 0.17%	-6.11% to 8.83%
Set 4	0.25% ± 0.24%	-5.40% to 4.03%
Set 5	0.57% ± 0.40%	6.16% to 5.72%
Set 6	0.15% ± 0.13%	-2.02% to 1.96%

Table 4: Mean difference between measured and calculated attenuation of treatment couch, its standard uncertainty and its range. The mean difference was calculated for both photon energies and both positions of rails.