Testing the recovered properties of simulated data using the spectral decomposition fitting method. Left: measured nuclear fraction, β, against the true value. The solid black line shows where the measured equals the true value. Right: measured nuclear optical depth, τ_N, against the true nuclear fraction. The solid horizontal lines show the true optical depth of τ_N = 4.5 in red and τ_N = 3.0 in blue. The vertical dashed black lines show a cutoff of β = 0.4, below which the measured values become unreliable.