Distribution of rms noises in the MWISP ¹²CO (1–0) observations (velocity resolution of ~0.16 km s⁻¹) toward the Crab Nebula. The unit of the scale bar is K. The relatively dark region shows the deep mapping area in the CO observations. The red ellipse shows the position and size (7′ × 5′) of the Crab Nebula, while the red dot at the center of the remnant shows the FWHM beam (52″) in the MWISP ¹²CO observations at the position of the pulsar ($l={184}_{\cdot }^{\circ }56,b=-5_{\cdot }^{\circ }78$).