In some examples, a printer determines a difference between an enlarged calibration pattern portion printed on a substrate by a first portion of a nozzle array of the printer and an enlarged reference pattern portion printed on the substrate by a second portion of the nozzle array, the enlarged calibration pattern portion produced by printing respective smaller calibration pattern portions at corresponding different relative positions between the nozzle array and the substrate, and the enlarged reference pattern portion produced by printing respective smaller reference pattern portions at corresponding different relative positions between the nozzle array and the substrate. The printer adjusts at least one drive signal to at least one of the first portion of the nozzle array and the second portion of the nozzle array to compensate for the determined difference.