We computed the variance 〈x2〉- 〈x〉2 of the operator x=EqE-q in which Eq=ΣSr·Sr+1eiqr for a one dimensional classical Heisenberg chain. We show that (〈x 2〉-〈x〉2)/〈x〉2 is of order 1, not of order 1/N as expected for a thermodynamic variable. This differs from earlier reported results for this variance. We find a similar result for the one-dimensional Ising and x-y models and establish a general condition for the correlation functions which causes such a result to oaccur. The large variance means that numerical calculations of 〈EqE -q(t) 〉 must be done carefully to produce reliable results. We introduce a new method to calculate 〈EqE-q(t) 〉 which avoids this problem. The method gives excellent results for the known values at t=0. We present results for 〈EqE-q(t) 〉 using this new method. They contain some features which are not yet fully understood.