Distribution of MBHBs per deg² as a function of magnitude. The vertical dotted and dashed lines correspond to the limiting magnitude of single and 10 yr co-added exposure modes, respectively. The dashed lines illustrate the cumulative probability functions of the full P_obs ≤ 5 yr MBHB population. In each panel, we show the number of MBHBs that are detectable in a single LSST exposure (N_det,  k,  k ∈ { u,  g,  r,  i,  z,  y }).