UCLES has two gratings, one with 31.6 and the other with 79 lines mm
,
both producing the same dispersion. The 79 lines mm
grating has 2.5 times
the free spectral range (FSR) and order separation, but less complete wavelength
coverage.
The resolving element in UHRF is a 31.6 lines mm
R2 204
408 mm
echelle grating, blazed at 64
.95 (measured).
See appendices 
, , and
for tabulations of order separations.