The insertion of a fourth dimension to the somatotype scheme is my main contribution. I have explained my reasons for the necessity of a measurement of degree of balance between the three general body dimensions on my blog site. (See The Significance of Centered Body-Types) This revision of the somatotype notation includes the degree of balance placed in parenthesis, after the usual three numbers separated by commas as follows: 
There is no need to learn the method of finding the degree of balance unless you are curious. All of the somatotypes on the male and female charts have the balance dimension already figured out. However, if you are conducting research you should probably know how this particular index is calculated so you can see that it is a potentially valid dimension that can be determined objectively.
The balance dimension is placed in parenthesis as a reminder that it is a derivative calculation that clarifies a special relationship between the main dimensions. You don’t have to stretch your conceptual muscles by conjuring up some solid geometrical model to produce the “balance” index. It involves very simple arithmetical operations. So let’s do it in steps.
Step 1. Express each component as a percentage of the sum of the three components. Example: 3,5,4 = 3 ÷ (3+5+4) = .25 5 ÷ (3+5+4) = .42 4 ÷ (3+5+4) = .33
Step 2. Subtract each of these percentages from .33 and express as an absolute value (without negative signs). Example: .33 – .25 = .08 .33 – .42 = .09 .33 – .33 = 0
Step 3. Add these figures Example: .08 + .09 + 0.0 = .17
Step 4. Next construct a table dividing up the two possible extremes of 4,4,4 = 0 and 1,1,7 (1,7,1 or 7,1,1) = .89 into 13 parts.
Step 5. Find where the number fits into the table below.
0.0 To .068 = 7.0
.069 To .137 = 6.5
.138 To .205 = 6.0
.206 To .274 = 5.5
.275 To .342 = 5.0 .
343 To .410 = 4.5
.411To .479 = 4.0
.480 To .547 = 3.5
.548 To .615 = 3.0
.616 To .684 = 2.5
.685 To .752 = 2.0
.753 To .821 = 1.5
.822 To .890 = 1.0
Example: .17 = 6.5
That’s all there is to it.
