Release 20150316 Summary of changes: CLC: The NuSTAR CLC files have been adjusted to improve the gain calibration for all pixels and grade combinations over the entire mission. Corrections vary grade-by-grade, but in general the absolute energy scale shifts by less than ~80eV and the gain shifts by less than 0.1% in most cases. This improves on the calibration done on 2014/04 and delivered in the CALDB 20140414. GAIN: A gain decrease of roughly 0.2% per year (shifting the energy of photons to lower energy) has been observed in the NuSTAR data. We have introduced a time-dependent correction in the energy calibration to account for this drift. As always, we recommend that all users re-process their data with the new calibration files to obtain the most accurate results. For users who have downloaded the Level 2 (calibrated and cleaned) event data via the HEASARC, we recommend checking the ÒCALDBVERÓ keyword in the FITS file header. If the CALDBVER listed is earlier then 20150316 then we recommend reprocessing the data with the latest calibration files. We expect that the changes to the calibration to only be apparent for observations obtained after mid-to-late 2013 and that also have high signal-to-noise or for analyses where the data are being jointly fit with a soft X-ray instrument (Chandra/Suzaku/Swift/XMM). We recommend quoting a systematic uncertainty of 40 eV in the absolute energy scale when performing line centroid fits at low energy, and a systematic uncertainty of 60 eV at for line energies around 68 keV. This uncertainty should be quoted in addition to the statistical errors (e.g. not added in quadrature with statistical errors) for clarity. A memo describing the calibration analysis and the systematic errors can be found here: http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/nustar/docs/fpm/index.html CLOCK: The latest version of the clock file contains all corrections during the mission up to 2015-03-13 and is required when using barycorr to correct the arrival times of the individual photons.