Artificial data inversion results for a variety of radial distances (from top to bottom, , 0.8 R, 0.9 R, 0.95 R and 0.98 R) and latitudes (from left to right, latitude 0°, 30° and 56°), for GONG (dotted curves) and MDI (dashed curves.) The solid curves show the ‘true’ rate and the thinner dashed and dotted curves represent 1σ error bounds on the inversion results.