Examples of Hess diagrams obtained during a typical run of StarFISH – in this case, for subregion G1 of tile 8_3, with  mag and A_V = 0.32 mag. From left to right we show Hess diagrams for a) the original VMC data, within the magnitude and colour limits used in this work, b) the best-fitting model derived by StarFISH, c) the χ² map, that is the fractional contribution of each CMD bin to the total χ², d) the difference between data and best-fitting model. In panels a), b) and d), the scale is in units of stars per CMD bin.