Position and error bars of the PG1159 star WD1 in the Kiel diagram together with all known objects of this spectral class. Also shown are the positions of other hot helium-dominated objects, namely DO white dwarfs and O(He) stars. Evolutionary tracks by Althaus et al. (2009) are labeled with the stellar mass in solar units. The black line indicates the PG1159 wind limit according to Unglaub & Bues (2000), meaning that the mass-loss rate of the radiation-driven wind at this position of the evolutionary tracks becomes so weak that gravitational settling of heavy elements is able to remove the heavy elements from the white dwarf atmosphere. Thus, no PG1159 stars should be found at significantly cooler temperatures. The dashed line is the wind limit assuming a mass-loss rate that is ten times lower. The fact that many PG1159 stars and DO white dwarfs are located at (half-)integer log ɡ values is an artifact due to the spacing of model atmosphere grids employed for spectral analyses.