Shower maxima obtained from gamma-ray simulations. Left: Profile of shower maxima as a function of the logarithm of energy. The left axis shows the slant depth traversed and the right axis the corresponding altitude above sea level. Right: Bias and resolution of the reconstructed height of shower maximum as a function of the simulated shower maximum. The top plots show fully detected and reconstructed showers at low zenith angles, below 35°, and the bottom row at high zenith angles, 60°.