Left: average monthly sensitivity curves for Gr#11, Gr#13 and Gr#16, derived from spectrophotometric standards taken during the first year of PESSTO observations. The thick lines are annual sensitivity function. Thin lines are monthly averages (Gr#11 offset by − 1, Gr#16 offset by +1 for legibility) Right: as a comparison, the sensitivity curves from individual standard stars over ten nights in March 2013 (for Gr#13). Four different standards were observed, L745a, LTT3864, EG274, GD71. The master sensitivity curve for March 2013 with this configuration is shown in black.