Hello, I am talking with someone online about buying their tank, however they are not a diver and do not know the cubic footage, this is what is know, it is an LP steel tank with 2250 psi stamped on it and a plus sign (by the way is the plus sign have significance?). The tank is 27' high(no valve) and 7' diameter. If anyone can find the cubic footage from this data please let me know, or if there is another marking on the tank which tells the volume of it.