Effect of spirals in biasing the bar length. Left panels: contours of constant surface density at two different times. Magenta points denote the orientation of the phase-angle of the m = 2 Fourier moment. Dashed circles denote different bar length measurements. Middle panels: radial variation of the m = 2 Fourier coefficient (normalised by the m = 0 component). Maroon dashed line denotes the value of R_bar, 2 whereas blue dashed line denotes the value of R_bar, 3. Right panels: radial variation of the phase-angle (ϕ₂) of the m = 2 Fourier moment. The magenta dashed line denotes the value of R_bar, 1. For further details, see the text. Presence of a spiral arm leads to an overestimation of bar length by ∼10 − 15% in our fiducial bar model.