ionized calcium reference ranges

I am working in a new facility and had a patient not doing well (lots of stuff going on). One of the nurses came in my room this am and told me the ionized calcium was 3.02, and I was pleasantly surprised, as her total calcium was low. She looked at me like I had 2 heads and said "UH... that's critically low". We were too busy to get into a discussion as we were intubating and she had blood pooring from her nose and stomache, but where I came from any thing over 1.9 was pretty good. So I said it must be the units we use that are different like mg/dl. I come home and research it this am, and we used mmol/liter and they use mg/dl. Big difference. I just though it was interesting, and good to know.