From John Macdonald, elog, 4 November 2002:
http://midtwist.triumf.ca:8081/EL/021104.4438?exp=twist
[slight edit by Rob MacDonald]

According to the solenoid operating manual the "safe" operating ranges for
LN2 and LHe levels in the cryostat are:
                       LN2             LHe
minimum safe level    120 l. (21%)    400 l. (50%)
preferred minimum     345 l. (60%)    560 l. (70%)
maximum (capacity)    575 l. (100%)   800 l. (100%)

We will continue our current practice of maintaining LHe above 70% and LN2
above 60%, but we should also be aware where the "red lines" are.

Our average boil-off rates over the past month have been:
                      3.2 %/day        1.2 %/day