  Globular clusters offer ideal laboratories to test the predictions of stellar
evolution. When doing so with spectroscopic analyses during the 1990s, however,
the parameters we derived for hot horizontal branch stars deviated
systematically from theoretical predictions. The parameters of cooler, A-type
horizontal branch stars, on the other hand, were consistent with evolutionary
theories. In 1999, two groups independently suggested that diffusion effects
might cause these deviations, which we verified subsequently. I will discuss
these observations and analyses and their consequences for interpreting
observations of hot horizontal branch stars.
