  We present Xspect, a method to obtain estimates of the angular power spectrum
of the Cosmic Microwave Background (CMB) temperature anisotropies including
analytical error bars developed for the Archeops experiment. Cross-power
spectra are computed from a set of maps and each of them is in itself an
unbiased estimate of the power spectrum as long as the detector noises are
uncorrelated. Then, the cross-power spectra are combined into a final
temperature power spectrum with error bars analytically derived from the
cross-correlation matrix.
  This method presents three main useful properties : (1) no estimation of the
noise power spectrum is needed, (2) complex weighting schemes including sky
covering and map noise properties can be easily taken into account, and
corrected for, for each input map, (3) error bars are quickly computed
analytically from the data themselves with no Monte-Carlo simulations involved.
Xspect also permits the study of common fluctuations between maps from
different sky surveys such as CMB, Sunyaev-Zel'dovich effect or mass
fluctuations from weak lensing observations.
