I'm trying to figure out some things regarding leak rates. I have a system which is constructed to adhere to UHV standards (total leak rate < 10^-10 Torr*L/s), baked out and evacuated to 10^-9 Torr, and then backfilled to about 600 Torr with N2 and Xe. So, there's a leak of air from the outside world to the lower pressure. I'm wondering how to calculate this leak rate. If I were at 10^-9 Torr, I'd just use the stated leak rate. I'd also be able to use a pressure rise measurement. But what about at higher pressure? I'd imagine that the leak rate is now less than 10^-10 Torr*L/s since there's a smaller pressure differential. Any way to calculate the leak rate at this pressure given the leak rate at UHV? I can't do a pressure rise measurement here because the leak rate is many orders of magnitude smaller than my base pressure.