Simulated CMDs using models of Marigo & Girardi (2007) that demonstrate the power of HeBs as chronometers of SF within the last ~1 Gyr. Panels on the left were constructed using a constant SFR (0.005 M_⊙ yr⁻¹), while panels on the right represent a ramped up SFR (0.005–0.1 M_⊙yr⁻¹). The stars are color coded by age and middle and bottom panels are plotted in opposite order. The points are plotted in reverse order to demonstrate the physical reality that HeBs, particularly BHeBs, of different ages do not have overlapping magnitudes and colors, making them very accurate chronometers for recent (<1 Gyr) SF. In contrast, MS stars of different ages can overlap in magnitude and color, which provide limited leverage on SF over the past ~1 Gyr.