To be really into the pole vault, one should have a minimum of three to five poles depending upon experience.
In the beginning, you may only have the budget for one pole. This one should be no longer than 1 foot over what you are trying to jump, and it must it be able to handle 4.4 lbs. (2 kilos) above your weight. As you progress, your first pole, if kept in good condition, can be your "BLUE POLE", and eventually the "GRAY POLE" in time. The "RED POLE" then can fill the role of being your "GREEN POLE" as described in items 2. and 3. above. Then as you progress, you will develop the confidence to throw everything at the bar with a new "RED POLE" when you feel that surge of adrenalin and assurance that the goal can be yours.
To explain this process, we convert imperial to a Metric number such as 2.2 lbs equals 1 kilo. Kilo divided by 2.2= lbs. Always round up when using this method converting back to imperial!
Having the poles 4.4 lbs or 2 kilos or .8 flex numbers apart is the best until you get to the end of the season then 2.2 lbs or 1 kilo or.4 flex numbers differential may be more appropriate as you go higher in smaller increments. As you get to pole over 200 lbs., one must realize that a system of measure that is suppose to be perfect and uniform will have its flex numbers worth more stiffness as the measure becomes less of a measurement and you may use .2 flex numbers as a differential spread. In other words, as the number gets smaller, 2 flex numbers will be much more stiffness than a flex number in the middle of the scale. So if you are working beyond 200 lbs. on a pole, select your poles closer together more like 2.2 or even by flex numbers of .2 if you can afford more poles.
This concept complies with National Federation High School rules on pole rating and works best when the vaulter selects a pole that is rated over their weight. Another requirement is that the vaulter must be holding in the grip area, no higher than 6" from the top of any pole or no lower than 18" from the top of the pole. This is very important for developing proper technique and efficient timing on the pole. Keeping the hand grip closer to the height that the vaulter jumps is important in the development stages for good technique. Most pole manufacturers are producing their poles with 5 lb. increments (light to heavy models with varying flex numbers). You, as the athlete or coach probably do not know what those numbers mean or where they fall in the light, medium, or heavy ranges of the 5 lbs. increment. Once you get a variety of poles then the flex number will be apparent to you within the same lengths.