2-Point Correlations in the COBE DMR 4-Year Anisotropy Maps
  The 2-point temperature correlation function is evaluated from the 4-year COBE DMR microwave anisotropy maps. We examine the 2-point function, which is the Legendre transform of the angular power spectrum, and show that the data are statistically consistent from channel to channel and frequency to frequency. The most likely quadrupole normalization is computed for a scale-invariant power-law spectrum of CMB anisotropy, using a variety of data combinations. For a given data set, the normalization inferred from the 2-point data is consistent with that inferred by other methods. The smallest and largest normalization deduced from any data combination are 16.4 and 19.6 uK respectively, with a value ~18 uK generally preferred. 
G. Hinshaw, A.J. Banday, C.L. Bennett, K.M. Gorski, A. Kogut, C.H.   Lineweaver, G.F. Smoot & E.L. Wright