A POS terminal determines an upsell to offer in exchange for the change due to a customer in connection with a purchase. Then, combining the covalently attachable labeling reagent with a mixture containing the molecule, under conditions wherein the labeling reagent has reactivity with the molecule thereby forming a covalent bond. Aspects of the invention include a color-coding system for water blasting gun safety; tools for the proper assembly of a water blasting guns; gun components having a safety code; and computer systems for asset-tracking, job safety analysis, and instruction that promote the safe use of water blasting guns. The processor in some such systems has an associated local memory to store the user input, the set of lighting atmosphere settings, and the identifier of the associated user.