The evolution of the raw sensitivity of CMB experiments
CMB-S4 Science Book, First Edition (arXiv:1610.02743)
Plot illustrating the evolution of the raw sensitivity of CMB experiments, which scales as the total number of bolometers. Ground-based CMB experiments are classed into Stages with Stage II experiments having O (1000) detectors, Stage III experiments having O (10,000) detectors, and a Stage IV experiment (such as CMB-S4) having O (100,000) detectors. Figure from Snowmass CF5 Neutrino planning document.