The AAR, sometimes denoted AAR0, of a glacier with a mass balance equal to zero. Glaciers do not in general have mass balances equal to zero. The Balanced-budget AAR is usually estimated as the AAR at which a curve (often linear) fitted to a relation between AAR and the Annual surface mass balance Bsfc, observed over a number of years, crosses the axis Bsfc = 0. The AAR0 of non-calving glaciers has been found to vary roughly between 0.5 and 0.6 on average, although the range of variation is substantial. On calving glaciers it is typically larger, approaching 1.0 on the Antarctic Ice Sheet. AAR0 can exceed 0.8 on tropical glaciers of year-round ablation type. The Balanced-budget AAR may differ from the steady-state AAR because it summarizes observations made in conditions that may not approximate to steady state.