InLine Pressure Jigs are relatively new in the mineral processing industry. By nature they posses a greater number of control variables than other gravity classifiers. The pulse action is complicated and can alter substantially in nature with just a minor adjustment to one of these variables. Three main aspects of the pulse can be discerned and these are, pulse stroke length (amplitude), pulse frequency (wavelength) and pulse a-symmetry (mode position). In this paper, the pulse is characterized into a single variable and it is correlated, along with other variables, to the efficiency of the unit, in a silica/calcareous-sea-shell classification application. (C) 2004 Elsevier Ltd. All rights reserved.