Radial profiles of the C¹⁸O line intensity (J = 3−2) considering different observational beams for a particular disk model (T Tauri star, M_disk = 10^-3M_⊙,f_small = 0.99). Different colors show different choices of the observational beam size. Solid lines represent the intensities obtained considering the isotope-selective processes (ISO network), dotted lines show the results when an approximative analysis is carried out (NOISO network). For the 0.1′′ and 0.5′′ beam, full lines are presented, whereas for the 1′′ and 3′′ beam they are binned at the spatial resolution. For the 3′′ beam, only the disk-integrated value (or the value that just resolves the outer disk) is shown.