A computer-implemented service acts as an intermediary between merchant sites and users thereof, and enables the users to purchase items on the merchant sites without having to create accounts with such sites. If not, free printing is inhibited. Each item has one or more variables, which store data. An appendage at least partially located within the expansion chamber. Resistors are connected to the n-type wiring lines and the p-type wiring line in parallel to the photodiode.