  The two basic approaches underlying the metrology of attosecond pulse trains
are compared, i.e. the 2nd order Intensity Volume Autocorrelation and the
Resolution of Attosecond Beating by Interference of Two photon Transitions
(RABITT). They give rather dissimilar results with respect to the measured
pulse durations. It is concluded that RABITT may underestimate the duration due
to variations of the driving intensity, but in conjunction with theory, allows
an estimation of the relative contributions of two different electron
trajectories to the extreme-ultraviolet emission.
