A customer-operated ordering system may allow a customer to select and consummate a sale himself. The quickly growing number of components in modern complex systems often necessitates the introduction of abstractions, that render said systems manageable. The eyeglass retainer has connectors at both ends which connect to the temples of a pair of eyeglasses. A plurality of grapple teeth extend outwardly from the cross member. Each water-guiding element is placed between two respective filtering bags, and formed with an annular body, an axial opening defined in the annular body, and radial channels in communication with the axial opening. The bias reversing circuit may also cause the first electrical potential to fall with a longer time constant than that of the second electrical potential when power from the voltage supply is removed.