  We summarize the outcome of the 12th meeting of the International
Astronomical Consortium for High Energy Calibration (IACHEC), held at the UCLA
conference center in Lake Arrowhead (California) in March 2017. 56 scientists
directly involved in the calibration of operational and future high-energy
missions gathered during 3.5 days to discuss the status of the X-ray payload
inter-calibration, as well as possible ways to improve it. The "Thermal
Supernovas Remnant" (SNR) Working Group presented a recently published paper on
1E0102.2-7219 as a calibration standard in the 0.5-1.0 keV band. A new method
to measure the high-energy spectrum of the Crab Nebula and pulsar with NuSTAR
without using its optics may yield a new absolute flux standard in the 3-7 keV
band. A new ACIS contamination model - released with CALDB version 4.7.3 -
leads to a significant improvement in modeling the spectral, spatial, and
temporal properties of the contaminant. The first calibration results of the
scientific payload on board Hitomi confirm the excellent performance of the
instruments before the spacecraft operation problems leading to its loss.
Finally, the meeting discussed extensively a novel statistic approach to
formally identify in which direction the effective areas of different
instruments would need to be changed to bring them into concordance. This
method could inform future further calibration efforts.
