Medical no2 is what is used for all nitrous fill stations. there are 2 grades 67 percent no2 and 98 percent no2.
The 98 percent is just a little more but look what you are getting. You are paying enought to buy for 98 percent no2 every time you fill up, but you are only getting 67 percent no2.
Look at it this way when you fill up at your neighbor hood fill station your getting a bottle filled with 67 percent no2 and 33 percent air.
You ever wonder why your bottle empties so fast.
Plus 98 percent no2 hits hard as heck and is easier to tune.