Change the weighting function used in the calculation of chi-squared.
Syntax: weight [standard | gehrels | churazov | model ]
Standard weighting uses or the statistical error given in the input spectrum. Gehrels weighting uses , a better approximation when N is small (Gehrels, N. 1986, ApJ 303, 336). Churazov weighting uses the suggestion of Churazov et al. (1996, ApJ 471, 673) to estimate the weight for a given channel by averaging the counts in surrounding channels. Model weighting uses the value of the model, not the data, to estimate the weight.