  Astrophysics demands higher precision in measurements across photometry,
spectroscopy, and astrometry. Several science cases necessitate not only
precision but also a high level of accuracy. We highlight the challenges
involved, particularly in achieving spectral fidelity, which refers to our
ability to accurately replicate the input spectrum of an astrophysical source.
Beyond wavelength calibration, this encompasses correcting observed spectra for
atmospheric, telescope, and instrumental signatures. Elevating spectral
fidelity opens avenues for addressing fundamental questions in physics and
astrophysics. We delve into specific science cases, critically analyzing the
prerequisites for conducting crucial observations. Special attention is given
to the requirements for spectrograph detectors, their calibrations and data
reduction. Importantly, these considerations align closely with the needs of
photometry and astrometry.
