Peak luminosities (2–200 keV) of the LH states and the subsequent HS states in GX 339‐4 (triangles) in the three outbursts. Observations of the sources studied in YFK2004 are also shown. Filled circles: Aql X‐1; diamonds: 4U 1705−44; squares: XTE J1550−564. Distances used to estimate these luminosities are 8, 4, 7.4, and 6.0 kpc, respectively. The relative uncertainties in the measured luminosities are around 3% or less, and are not shown in the plot. A recent study of Aql X‐1 shows that the luminosity of the hard‐to‐soft state transition can be lower by a factor of 5, following the same linear relation (Yu & Dolence 2006).