A recent calibration of the ⁴⁰Ar/³⁹Ar geochronometer is based on an optimization analysis of ⁴⁰K activity data, isotopic data for the Fish Canyon sanidine (FCs) standard, and pairs of ⁴⁰Ar/³⁹Ar+²³⁸U–²⁰⁶Pb data from selected samples meeting well-documented quality criteria. Inclusion of ²³⁸U–²⁰⁶Pb data in the calibration incorporates the precisely known ²³⁸U decay constant. Thus, this calibration is inherently consistent with the U–Pb chronometer. Initial presentation of the calibration included an inappropriate datum and should be eschewed in preference to a revision. Compared with previous calibrations, including those focusing mainly on the age of a standard (e.g. astronomical calibrations), the optimization calibration provides superior accuracy in the sense of propagated age uncertainty, particularly for ages much older than the FCs. Recent literature reveals that the optimization-based calibration has been misused and misrepresented in some cases; discussion of these cases clarifies the correct usage of the approach. Apparent conflict between ⁴⁰Ar/³⁹Ar and ²³⁸U–²⁰⁶Pb ages for a Quaternary tuff do not appear to be a result of error in one of the three parameters determined by the optimization approach for the ⁴⁰Ar/³⁹Ar system. The optimization approach easily accommodates new constraints, but rigorous quality control is needed to maintain accuracy.