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Systematic electron microscopy of quasi crystals in an Al-14 at % Mn alloy has been carried out. High resolution imaging reveals fringes with spacings in the ratio of 1:τ. Besides 5-3-2 symmetry axes, other important zones of electron diffraction patterns are experimentally determined and compared with those generated by Landau generation technique and by projection technique. It has been shown that the 'T' phase, which often co-exists with quasicrystal, is closely related to it and can be treated as a two dimensional quasiperiodic crystal stacked periodically along an icosahedral vector of a true quasi crystal. Our results indicate that it is possible to have a general frame work of quasi periodic incommensurate modulation in three, two and one dimensions. The quasi crystal, the 'T' phase and vacancy ordered τ phases are the respective real life examples of such modulations.