A protective gas supply device for on-site supply of workplaces is provided, in which a liquid argon reservoir, a liquid oxygen reservoir or a liquid carbon dioxide reservoir, and a helium supply are connected to first and second mixers supplying gas to site workplaces. The tracked instrument can be used to simulate or visualize interactions with internal features of the physical object represented by the physical model. The optical device also includes a plurality of low index layers. Responsive to determining that the one or more data structures in JOIN include a parentchild relationship, the computer determines whether the query that includes the JOIN includes a filter applied on one or more data structures in the JOIN with an OR condition between filters. The energy of the number of halftone tile seams is determined according to an energy metric so as to provide indication of at least one low energy determined halftone tile seam. The blending apparatus further includes a lid to cover the cavity defined by the container, and an attachment to fit within the cavity and rotate about the center axis of the cavity.