Summary: We consider linear combinations of “natural” time scales and choose the “best” one which provides the minimum coefficient of variation of the lifetime. Our time scale is in fact a generalized Miner time scale [M. A. Miner, J. Appl. Mech. 12, A159–A164 (1945)] because the latter is based on an appropriate weighting of the times spent on low and high level loadings. The suggested modus operandi for finding the “best” time scale has many features in common with the approach suggested by V. T. Farewell and D. R. Cox [Appl. Stat. 28, 73-75 (1979)] and D. Oakes [Lifetime Data Anal. 1, No. 1, 7-18 (1995; Zbl 0821.62084)] which is devoted to multiple time scales in survival analysis.