Oz, my wife is taking the SDI online computer nitrox course for the exact same reason yours is I did not want her breathing air while I am breathing nitrox and screw up my diving when we go to Belize next month. When she finishes the course she will go to the shop review any questions she has missed and then test a couple of tanks and issue her permanent card right then and there. She apparently thought I was going to take the tests for her ( snicker ) but she got over that and is now actually learning it for herself and doing just fine.