Droplet size.

Droplet size is the volume of ink one nozzle ejects in a single firing, quoted in picolitres, and a head carries a native drop size before any greyscale mode is applied. Small drops buy fine features and smooth tonal gradations; large drops buy density, opacity and fluid volume per pass, which is what absorbent substrates and heavy laydown want. That trade is the point of greyscale heads, which vary the size of the drop fired or merge several drops so fine type and a solid fill can come off the same nozzle row in one job. Run the wrong drop mode and the solid comes off thin and grainy on blanks you have already loaded and printed, and the reprint costs you the garments as well as the press time.