Chemical evolution of the best-fit SFH for silicon of the inner disc using the solar abundances of Anders & Grevesse (1989). The grey lines are the results of the various bootstrapped best-fit SFHs, the black line is the mean value. Filled circles are the inner disc stars, empty circles are the outer disc from Haywood et al. (2013). In panel a) the green region is the standard deviation on the values in each bin. These values are not independent and the variance in the total SFH is considerably smaller than in each individual bin. Panels a)−d) show the best-fit SFH, the evolution of [Si/Fe] with age, the evolution of [Si/Fe] with metallicity, and the evolution of the metallicity with age.