Histogram of our sample binned by spectral type. B0, B0.2, and B0.5 spectral types have been grouped in the B0 bin, as with B0.7 and B1 in the B1 bin, and B2 and B2.5 in the B2 bin, whereas B1.5 remains ungrouped. The unfilled histogram shows the total number of stars in each bin, whereas the filled histogram shows the number of identified binaries, stacked and colour-coded by luminosity class. Multiplicity fractions for each luminosity class have also been added as annotations, whereas the total multiplicity fraction is shown at the top.