  We show that diffraction intensity into the First Order Laue Zone (FOLZ) of a
crystal can have a strong azimuthal dependence, where this FOLZ ring appears
solely because of unidirectional atom position modulation. Such a modulation
was already known to cause the appearance of elliptical columns in atom
resolution images, but we show that measurement of the angle via 4-dimensional
Scanning Transmission Electron Microscopy (4DSTEM) is far more reliable and
allows the measurement of the modulation direction with a precision of about
1{\deg} and an accuracy of about 3{\deg}. This method could be very powerful in
characterising atomic structures in 3 dimensions by 4DSTEM, especially in cases
where the structure deviates from that found in bulk crystals.
