You are doing what the other poster suggested comparing apples to oranges. I am NOT comparing 3 to 4, or 4 to 3, or 4 to 4+. I am comparing 4 to 4 and the volume. Doubling time may not be possible to calculate. Ignore volume so a doubling time can be calculated is what I think you are saying, again that is good information but here is a simple fix to make the system relevant today. Then in your example, are you talking doubling time of the 3 or the 4 since you mix 3 and 4 and I am comparing only 4 to 4?