A method of assembling multi-pane insulating glass units (IGUs) comprising: (a) creating a manufacturing schedule for assembly of a plurality of insulating glass units from spacer frames and glass lites, said manufacturing schedule including both double pane insulating glass units and triple pane insulating glass units; (b) providing first and second conveyors for moving glass lites or panes along controlled travel paths extending into and through a washer to at least two different registration stations where lites are brought into registration with each other; and (c) if the manufacturing schedule next designates assembly of a triple pane insulating glass unit: (i) moving a first outer glass lite and a first spacer frame registered with the first outer glass lite on a conveyor to a first registration station as a unit and registering a middle lite with the first spacer frame and first outer glass lite to form an intermediate IGU layer, (ii) moving the intermediate IGU layer to a different registration station other than the first registration station, and (iii) at the different registration station moving a second, outer lite and second spacer frame into registration with the intermediate IGU layer to form the triple pane insulating glass unit; or (d) if the manufacturing schedule next designates assembly of a double pane insulating glass unit, moving a first outer glass lite and a first spacer frame registered with the first outer glass lite to a selected one of the two registration stations where a second outer lite is brought into registration with the first spacer frame to form a double pane insulating glass unit, characterized in that a plurality of lites are staged at an entry position to the washer, and wherein a user is prompted in accordance with the manufacturing schedule by a visual indicator of the order in which to place given lites from the plurality of lites onto the first and second conveyors that extend into and through the washer. (a) creating a manufacturing schedule for assembly of a plurality of insulating glass units from spacer frames and glass lites, said manufacturing schedule including both double pane insulating glass units and triple pane insulating glass units; (b) providing first and second conveyors for moving glass lites or panes along controlled travel paths extending into and through a washer to at least two different registration stations where lites are brought into registration with each other; and (c) if the manufacturing schedule next designates assembly of a triple pane insulating glass unit: (i) moving a first outer glass lite and a first spacer frame registered with the first outer glass lite on a conveyor to a first registration station as a unit and registering a middle lite with the first spacer frame and first outer glass lite to form an intermediate IGU layer, (ii) moving the intermediate IGU layer to a different registration station other than the first registration station, and (iii) at the different registration station moving a second, outer lite and second spacer frame into registration with the intermediate IGU layer to form the triple pane insulating glass unit; or (i) moving a first outer glass lite and a first spacer frame registered with the first outer glass lite on a conveyor to a first registration station as a unit and registering a middle lite with the first spacer frame and first outer glass lite to form an intermediate IGU layer, (ii) moving the intermediate IGU layer to a different registration station other than the first registration station, and (iii) at the different registration station moving a second, outer lite and second spacer frame into registration with the intermediate IGU layer to form the triple pane insulating glass unit; or (d) if the manufacturing schedule next designates assembly of a double pane insulating glass unit, moving a first outer glass lite and a first spacer frame registered with the first outer glass lite to a selected one of the two registration stations where a second outer lite is brought into registration with the first spacer frame to form a double pane insulating glass unit, characterized in that a plurality of lites are staged at an entry position to the washer, and wherein a user is prompted in accordance with the manufacturing schedule by a visual indicator of the order in which to place given lites from the plurality of lites onto the first and second conveyors that extend into and through the washer.