Isochrones at 8 Gyr and [Fe/H] = –0.5 for three different HST-WFC3 CMDs. The panels demonstrate the effect of varying [α/Fe] on the bolometric corrections (BCs) and the underlying isochrones. The left column shows the effect of varying [α/Fe] in the BCs while keeping the underlying isochrones fixed at [α/Fe] = +0.2. The middle panel shows the effect of varying [α/Fe] in the isochrones while leaving the BCs fixed at [α/Fe] = +0.2. The right panel shows the combined effect of varying both components together.