Comparison of mean magnitudes determined from literature MV15 to new IMACS light curves in the V band (blue circles, left) and I band (orange squares, right). Sources that were observed for only one epoch with IMACS were removed and a further 3σ clip is applied. Clipped RRLs are denoted with an open gray circle. Residuals are shown in the bottom panel and the average and standard deviation of the offsets are ΔV = 0.003 ± 0.053 and ΔI = 0.03 ± 0.04 mag.