It should not be allowed to warm up more than 10 K, otherwise the detector temperatures will being to change and thermal gradients will be set up in the internal optical bench. The LN 2 should be filled twice a day, once in the very late afternoon just before dinner and again at the end of the night. It is occasionally necessary to do a refill before dawn in this case. There are markings on the dome floor showing where the platform should be driven to so as to be in approximately the correct position when it is raised to the height of the instrument. Ideally, the transfer tube should be almost horizontal.
Extreme care is required when the platform is rising.
It is very easy to hit something or trap a cable. Extreme care is also required when withdrawing the plastic tube from the Gemini LN 2 can, since it will be frozen solid and very brittle. It is best to wait a few minutes to allow the tube to warm up. Use two gloved hands to ease it out slowly. To execute the fill once the tube is inserted, simply open the valve on the big canister.