Multiple instruments can share a communications cable, so each complete instrument has an identifying ASCII “tag” that helps in software communication. Multichannel BICs use the lower case letters “a” to “z”.  Single channel instruments, such as the QSL, use numerical tags (1–9). During manufacture, an individual BIC normally has the tag set to “a”, and a single channel instrument is typically set to tag 2. Orders for multiple systems increment the tag in a sensible order (a, b, c, etc., or 2, 3, 4).