Left-hand panel: best fit by eye for the line core (solid red line, log n(⁴He+³He) = −2.50) and the line wings (dotted red line, log n(⁴He+³He) = −1.79) of He I 4026 Å in the HRS spectrum of PHL 25 (solid black line). Right-hand panel: same as the left-hand panel, but for He I 4472 Å. The total helium abundances are log n(⁴He+³He) = −3.00 (solid red line) and log n(⁴He+³He) = −2.10 (dotted red line).