Need help interpreting this equal fittings chart So I know t

Need help interpreting this equal fittings chart!!!

So I know this a chart used in order to calculate equivalent lengths for various fittings. But I dont know what several things on here mean. For instance, I know L/D is the length of the duct over the diameter. But why are there different numbers under that column if L and D are variables????

Also, on the other columns you have 6(15) 8(20) 10(25) and so on. What does the number outside the parenthesis mean and what does the number inside of it mean?

Solution

* In 6(15), 8(20), 10(25), 12 (30) number outside the parenthesis denotes diameter in inches.

and the number inside the parenthesis denotes the diameter in centimeter

* 8 (2.4), 10 (3.1), 13 (4.0), 15 (4.6), etc.. denotes the equivalent length. In this the number outside the parenthesis denotes equivalent length in feet and the number inside the parenthesis denotes the equivalent length in meters.

* The first column denotes the approximate L/D ratios for the particular row.

Eg.: In the first row, for pleated elbow, 90 deg, (2.4 m / 15 cm) = (3.1 m / 20 cm) = (4.0 m / 25 cm) = (4.6 m / 30 cm) 15 (L/D)