U : Sound and Vibration Terms, Definitions, Units, Measurements ..
UKAS - United Kingdom Accreditation Service : is the national accreditation body recognised by government to assess, against internationally agreed standards, ...
Ultrasound : frequencies above the audible range, that is over 20 kHz.
Undamped Natural Frequency : the natural frequency of a structure.
Under-range : the input to the Sound Level Meter is too low for the current measurement range. Change the range.
Under-range % : percentage of time an under range occurred