X-unit

x-unit

n
(Units) a unit of length equal to 0.100 202 × 10–12 metre, for expressing the wavelengths of X-rays and gamma rays

X-unit

(x or XU) A unit of length used especially for measuring wavelength. 1 x-unit ! 10-3 ångström (10-13 m).
References in periodicals archive ?
The machines involve less welding, in favour of bolts, and the X-unit is bolted to the chassis, rather than welded.