A rotatable and retractable rear gun sight is disclosed. The Internet standard TCP protocol implements two algorithms for that: an original one based on a special timer, and a later addition to TCP that is triggered when there are three packets received by the client after the missing one. The connected LED PCBs may be configured in a light tube that includes connector end caps for mounting the light tube in a light fixture. The provision of pads complying with the minimum spacing requirements for both flip-chip and wire bond assembly enables a \u201cdual purpose\u201d die to be produced without any increase in die size. The central voltage measurement circuit and the voltage addition circuit shift a gate voltage of the MOS field-effective transistor by an amount equal to the deviation of a source voltage of the MOS field-effective transistor caused by an input offset voltage Voff. The inventory provider communicates with the PLC and reserves for the ordered product a vacant storage compartment.