  One of the challenges related to stellar bars is to accurately determine the
length of the bar in a disc galaxy. In the literature, a wide variety of
methods have been employed to measure the extent of a bar. However, a
systematic study on determining the robustness and accuracy of different bar
length estimators is still beyond our grasp. Here, we investigate the accuracy
and the correlation (if any) between different bar length measurement methods
while using an N-body model of a barred galaxy, where the bar evolves
self-consistently in the presence of a live dark matter halo. We investigate
the temporal evolution of the bar length, using different estimators (involving
isophotal analysis of de-projected surface brightness distribution and Fourier
decomposition of surface density), and we study their robustness and accuracy.
We made further attempts to determine correlations among any two of these bar
length estimators used here. In the presence of spirals, the bar length
estimators that only consider the amplitudes of different Fourier moments (and
do not take into account the phase-angle of m=2 Fourier moment) systematically
overestimate the length of the bar. The strength of dark-gaps (produced by
bars) is strongly correlated with the bar length in early rapid growth phase
and is only weakly anti-correlated during subsequent quiescent phase of bar
evolution. However, the location of dark-gaps is only weakly correlated to the
bar length, hence, this information cannot be used as a robust proxy for
determining the bar length. In addition, the bar length estimators, obtained
using isophotal analysis of de-projected surface brightness distribution,
systematically overestimate the bar length. The implications of bar length
over(under)estimation in the context of determining fast and slow bars are
further discussed in this work.
