When using equipment where errors in estimating RHmin can be large, or when RH data integrity are in doubt, then one should use only RHmax.
cal_ActualVapourPressure_from_RHmax(Tmin, RHmax)
A vector for actual vapour pressure
daily minimum temperature (degrees Celsius).
maximum relative humidity (%).
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. FAO Irrigation and drainage paper No. 56. Rome: Food and Agriculture Organization of the United Nations, 1998.