Analysis of the ratio map of NGC 5406. Panel a: observed i-band SDSS image of the galaxy with north up and east left. The dotted ellipse indicates the region of the galaxy considered for the deprojection. The galaxy inclination is given. Panel b: deprojected image of the galaxy. The red and blue crosses correspond to the peaks measured in the Q_T(R_Qb) and Q_T(R_mean) azimuthal profiles, respectively. Panel c: map of the transverse-to-radial force ratio Q_T(r, ϕ). The vertical blue and red lines indicate the location of R_Qb and R_mean, respectively. The bar strength is given. Panel d: radial profile of ⟨Q_T⟩. The vertical dotted line corresponds to the boundary of the bulge-dominated region, identified as the range from the centre to the minimum (or a change in the slope) in the ⟨Q_T⟩ radial profile. The vertical blue and red lines indicate the location of R_Qb and R_mean, respectively. The horizontal red segment represents the error associated with R_Qb. Panel e: azimuthal profile of Q_T(R_Qb). The local maxima of the profile are highlighted by red asterisks. The horizontal dotted line corresponds to the threshold value at Q_T = 0.05, adopted to count the number of peaks associated with the bar. The value of R_Qb from this paper is given. Panel f: azimuthal profile of Q_T(R_mean). The local maxima of the profile are highlighted by blue asterisks. The horizontal dotted line corresponds to the threshold value at Q_T = 0.05, adopted to count the number of peaks associated with the bar. The value of R_mean from literature is given.