Absolute brightness changes in the uvw2 filter as function of time between two UVOT pointings for all 25 sources with multiple observations. The black crosses show the median values (and median absolute deviation) and the grey dots mark all 174 pairs of observations. While micro-variability (Δm_uvw2 ≈ 0.1 mag) dominates on time scales shorter than 50 d, significantly larger variability (Δm_uvw2 > 0.3 mag) is observed at Δt > 50 d.