The small compressor is on top of the gas mixing rack (left side, small gray box).

The O2 analyzer is on top of the TOF rack (above the tofgas PC)

1. On the PC, turn ON SV10 (ref.gas).
2. On the return line, open 3-way valve (it is above the small compressor).
3. Turn ON small compressor (black switch on the gray box).
4. Open OUT, and then IN, valves of O2 analyzer.

To turn OFF the small compressor
1. Close IN and then OUT O2 analyzer valves
2. Turn OFF small compressor
3. Close 3-way valve
4. Turn OFF SV10