They include 4-inch (101.6-mm) diameter transmission spheres with f/numbers of f/0.75, f/1.5 and f/3.3, with λ/40 PVr (λ = 633 nm) surface form. Other 4- and 6-inch Ultrasphere transmission spheres are available.
Each Ultrasphere transmission sphere includes absolute calibration of the reference surface, and are shipped with the resulting MetroPro *.dat file and 37-term Zernike fit on a USB memory stick.
Download the spec sheet for additional details.
* Assumes form metrology of smooth spherical surfaces, a well-nulled cavity, data averaging to minimize systematic noise, a suitably stable environment, and uncertainty estimation following ISO's "Guide to the Expression of Uncertainty in Measurement" (1995) with k=1.
PVr is defined as the 36 term Zernike fit plus 3 times the rms residual of the Zernike fit.