A wireless cryptographic fill system includes a fill device and a host portion. The delegation scheme may be rules-based and may be applied to a single real-time communication channel or multiple communication channels, including both real-time and non-real-time communication channels. In this case, the RF anti-reflection coating can be a layer of silicon dioxide, which can be sandwiched between two IR anti-reflection coatings designed to minimize IR reflections between the surrounding air and the RF anti-reflection coating and between the RF anti-reflection coating and the prism material, respectively. If such a free block is not found, a block at least as large as the request size maybe split and the request satisfied with the resulting split block. The capo comprises a bar assembly for extending across and engaging the strings on the neck of an instrument, and a spring assembly connected to opposite ends of the bar assembly and extending across the back of the neck of the instrument for pulling the strings into contact with the frets of the instrument.