The Weber is the unit of magnetic flux, or in layman’s terms, magnetic strength. It is an important measurement for getting signals on and off of magnetic tape (whether digital or analog). One Weber is much too large a unit to be relevant with tape recorders so the nanoweber (one billionth of a Weber) is standard unit of measurement. The recorded level of tape is expressed in nanowebers per meter of tape. Especially in analog recording the signal level to tape is a critical component in the performance of the tape. Too high a level and you get distortion and lack of headroom, but with too low a level your signal-to-noise ratio is compromised. The proper recording level for tape depends a lot on the formulation of the tape and the electrical/magnetic characteristics of the recorder. Recorders are thus aligned using standard reference tapes containing tones at known levels rated in nanowebers per meter. Once the machine is calibrated to a reference it becomes possible to optimize its levels for the particular formulation of tape desired through another alignment procedure.