Time-resolved observations of rotational modulations of brown dwarfs and directly imaged exoplanets provide tight and direct constraints on the properties of condensate clouds that are a key obstacle in understanding ultra-cool atmospheres. HST treasury program Cloud Atlas applies this technique to nineteen brown dwarfs and directly imaged exoplanets to statistically evaluate the effects of temperature and surface gravity on their clouds. I will present the latest Cloud Atlas light curves of two planetary mass/brown dwarf companions HN Peg B and 2M1207 b. We measure these companions’ spectral dependence of rotational modulations, especially in- and out-of-water band, and derive the vertical cloud structures in their atmospheres. We also examine the cloud property difference between these companions and field brown dwarfs. In addition, we developed HST/WFC3 IR detector model RECTE that conquers a major WFC3 systematics — ramp effect. This model can be widely adopted in HST/WFC3 transit spectroscopy and brown dwarf rotational modulation observations.