**Table 1:** Details of the observations of the Crab nebula with HESS between October 2003 and January 2005. For the purposes of this study, the data has been divided into 3 subsets.
Data Set	Date	$N_{{\rm tels}}$	Z range	$\langle {Z} \rangle$	Offset	$N_{{\rm runs}}$	Obs. Time	Live-time	Mean System rate
			( $\ensuremath {^{\circ }}$ )	( $\ensuremath {^{\circ }}$ )	( $\ensuremath {^{\circ }}$ )		(h)	(h)	(Hz)
I	10/'03-1/'04	3	45-55	46.6	0.5-1.5	12	5.3	4.8	179
II	1/2004	4	45-65	54.4	0.5-1.5	14	6.3	5.7	240
III	10/'04-1/'05	4	45-55	47.9	0.5-1.5	26	11.3	10.6	180
Total			45-65	50.2	0.5-1.5	52	22.9	21.1	196

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