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This isochron diagram shows the inferred 41Ca/40Ca ratio in the E44 CAI from the Efremovka meteorite. 20 years ago, the former existence of 41Ca (half-life = 0.1 Myr) was first demonstrated in this CAI, with the inferred 41Ca/40Ca ratio = 1.4e-8 (long dashed line). Reanalysis of K isotopes in the same CAI with an advanced secondary ion mass spectrometer revealed a 5-time lower 41Ca/40Ca ratio of 2.6e-9. This discovery has important implications for the origin of short-lived radionuclides in the early solar System.