Method of operating a sheet feeding device, said device comprising an elevator for a stack of sheets, and an air supply system configured to supply and direct one of more air streams towards an upper region of the sheet feeding device for floating a plurality of upper sheets of the stack of sheets, wherein the elevator comprises a vertically movable support for supporting the stack of sheets from below, wherein the sheet feeding device comprises an optical sensor positioned adjacent the floated sheets for measuring light reflected from the floated sheets at a plurality of different heights, characterised in that the method comprises the steps of: continuously deriving from the optical sensor a density reading indicating the density of sheets floated, continuously deriving an average density based on a plurality of density readings, continuously deriving an upper density limit based on the average density multiplied by a predetermined upper density limit factor (UDLF), continuously deriving a lower density limit based on the average density multiplied by a predetermined lower density limit factor (LDLF), adjusting a first operating parameter of the sheet feeding device should the density reading exceed the upper density limit, wherein the adjustment of the first operating parameter is such as to decrease the density of floated sheets, and adjusting the first operating parameter of the sheet feeding device should the density reading subceed the lower density limit, wherein the adjustment of the first operating parameter is such as to increase the density of floated sheets. an elevator for a stack of sheets, and an air supply system configured to supply and direct one of more air streams towards an upper region of the sheet feeding device for floating a plurality of upper sheets of the stack of sheets, wherein the elevator comprises a vertically movable support for supporting the stack of sheets from below, wherein the sheet feeding device comprises an optical sensor positioned adjacent the floated sheets for measuring light reflected from the floated sheets at a plurality of different heights, characterised in that the method comprises the steps of: continuously deriving from the optical sensor a density reading indicating the density of sheets floated, continuously deriving an average density based on a plurality of density readings, continuously deriving an upper density limit based on the average density multiplied by a predetermined upper density limit factor (UDLF), continuously deriving a lower density limit based on the average density multiplied by a predetermined lower density limit factor (LDLF), adjusting a first operating parameter of the sheet feeding device should the density reading exceed the upper density limit, wherein the adjustment of the first operating parameter is such as to decrease the density of floated sheets, and adjusting the first operating parameter of the sheet feeding device should the density reading subceed the lower density limit, wherein the adjustment of the first operating parameter is such as to increase the density of floated sheets. continuously deriving from the optical sensor a density reading indicating the density of sheets floated, continuously deriving an average density based on a plurality of density readings, continuously deriving an upper density limit based on the average density multiplied by a predetermined upper density limit factor (UDLF), continuously deriving a lower density limit based on the average density multiplied by a predetermined lower density limit factor (LDLF), adjusting a first operating parameter of the sheet feeding device should the density reading exceed the upper density limit, wherein the adjustment of the first operating parameter is such as to decrease the density of floated sheets, and adjusting the first operating parameter of the sheet feeding device should the density reading subceed the lower density limit, wherein the adjustment of the first operating parameter is such as to increase the density of floated sheets.