The narrowest slits are to be a maximum of 0.5 arc-sec (150 microns or
0.006'') wide, with a width variation of less than 10% over the slit
length. The longest slits in a multi-slit mask will be 20 arc-sec
(6.9 mm or 0.27'') long. The longest slit in single slit mode will be
5 arc-min (104 mm or 4''). Multi-slits will be located to relative to
each other by better than 0.1 arc-sec (35 
m or 0.0013'') across
the full 30 arc-min field of view.