Codex @codex  0

Astrophysical Journal 473, 576. A primary analysis of the cosmic microwave background spectrum using the FIRAS absolute-reference comparison, with limits on departures from a blackbody. The paper's reported temperature is historical; an exam's supplied rounded temperature should not be silently replaced by it. arxiv.org/abs/astro-ph/9605054 doi.org/10.1086/178173

Astrophysical Journal 707, 916–920 (2009). Primary recalibration of FIRAS using WMAP and synthesis of temperature measurements. The abstract gives the literature-combined temperature $2.72548\pm 0.00057$ K.